sad paradox indeed; however, if you can train the dog, things would likely be better. Your mom is likely torn, she doesn't want to lose the dog, but she doesn't want to be liable for any thing that may happen to a visitor. If you can show her that the dog has improved, she may be more willing to keep the dog.
I assume money is an issue if you are asking the MDb for help and thus a animal behaviorist may not be an option for you (though it is the best option). The next step to take would be attempting to re-train your dog yourself. This can be very tough especially if they've gotten into routines.
First you must properly identify the dogs behavior. Just because a dog jumps/barks/claws/nuzzles doesn't necessarily mean it's being aggressive. It also could be playful.
When the dog jumps or becomes 'agressive' does it start by growling? Does the dog bark in an aggressive way? Does the hair on the dog's spine stand up? These are all important things to look for in regards to aggressive/threatened behavior. Does your dog bark/jump on all of your friends or just certain ones? Does the dog attempt to bite your visitors? And if so, is it a playful biting (which can seem hard to a human) or is it aggressive?
Was the dog abused by it's previous owners? Usually this is easy to tell if your dog is very skittish around people to include yourself or other well known people in your household.
While determining the type of aggression is not crucial in re-training the dog, it's good to know. It helps you set boundaries on how hard you want to train the dog. An abused/aggressive dog may feel threatened if you attempt to train them hard or aggressively.
When you are ready to train your dog, you must first train them on what a 'reward' sound is and what a 'bad dog' sound is. Most people yell and play with their dogs in one tone or in tones that are too similar for your dog to comprehend and may not realize what is bad and what is good. So this is the first thing you want to do.
The Tone!Your tone is very important. Your dog is more prone to understanding your tone then anything else. While most dogs 'learn' what 'sit', 'stay', 'lay down', ect ect sounds like, it is your tone that is going to give away the severity of your command.
If you have ever listened to a dog, you will notice that most animals when playing or in a 'good mood' usually utilize medium-high pitched noises to express this up to and including a yelp of joy. As the trainer, you need to understand that. If the dog is hyper or playful, commanding your dog to do something in the same tone may not get the command across where a stern voice will.
So giving commands. Does your dog already know some commands like sit, stay? If so, then this is the easy part. First, change the way you say these commands dependent on the dogs behavior.
1. If you are playing with your dog or teaching it new commands, utilize a higher than normal talking voice when giving commands (almost like playing with a baby). The dog will respond better.
2. If your dog is being annoying (say barking at a passing car, or passerby), start your commands in a normal voice. The dog will understand this as you not playing or them to continue. If the dog continues with its behavior, repeat the command in a deeper more stern voice. This indicates to the dog that the behavior is bad. A firm "No" versus a high pitched "No" means two different things to your dog. If the behavior continues, a firm tap on the muzzle with the firm command should do the trick (I personally use physical means as a last resort, you don't want your dog scared of you. If you are against a 'firm tap' you can utilize other means of 'bad dog'.
3. The firm/stern voice should always be used when attempting to relay to your dog that something they have done is bad, and a medium-high pitched voice for anything rewarding.
The Treat!The first thing you want to do is pick up some dog treats as a reward. This will help your dog associate good behavior with food (always a dog's friend). You want to start your rewarding heavy. If the dog does something good on your command, give it a treat. Over the next few months, lessen the amount of treat rewards your dog receives (after all you don't want to make them unhealthy) and acquaint them with good behavior being your loving reply of "good boy" (a treat is still good if you are giving commands to keep the dog in tune with you).
Be sure to pet your dog and show physical approval of as rewards to. Your attention is usually what the dog loves best besides a treat
Bad Dog!Discipling your dog is very important. Anytime the dog does anything bad, you want to be sure they understand they have been bad. Be sure to use a stern "NO" or other command to relay your 'I mean it" attitude.
I personally try my hardest not to utilize physical contact with my dog when it comes to bad behavior. This is usually my last resort as a good tap on the muzzle will often get your point across. If you are against physical discipline, you can utilize other methods such as a spritz bottle or a ultrasonic emitter that only dogs can hear (these don't harm the dog, but creates an annoying pitch your dog doesn't like (though I've never heard it so I can't say for sure that's what they do). Check out below for a ultrasonic hand device.
http://www.moorepet-petdoors.com/PetSaf ... 100-19.htmIf your dog barks incessantly, you can also get a citronella dog collar that sprays the dog with citronella (not harmful, but unpleasant) every time it barks. Buy one that you can turn off or take it off when you don't mind him being playful; otherwise the dog will associate barking as bad all the time (and you don't want that), but great for when you have visitors and they become an unstoppable barking force.
Putting your dog in time out can also be effective. When the dog does something bad or does not listen to your commands, put them in a room for time out. They will associate bad behavior with the inability to be in your presence.
VisitorsSo the issue you are having is usually with visitors. What causes your dog to jump/bark on them. Most dogs get aggressive if they feel their owner is threatened. Do your friends play wrestle with you or run at you? If you are outside playing a sport, does he become aggressive. Does your dog go after them because he doesn't know them?
The first thing you need to do is introduce your friends to the dog, but not all at once. Ask a friend to come over and meet your dog. If your dog starts barking the second they walk in the door, begin the 'bad dog' discipline. This will indicate to them that the visitor is welcome in your house. If the dog does not calm down, ask your friend to leave (let them know in advance they may have to go if the dog doesn't calm down). If capable, have your friend come back as often as possible, being sure to introduce them to the dog and keeping up with the 'bad dog' routine until they learn they are welcome. Be sure your visitor does not attempt to give commands to the dog as this only confuses them (unless the dog is hurting or being overly aggressive).
Make sure that you or your visitor never cower to the dog. They will take this as a sign of weakness and it will only serve to further their bad behavior or become more aggressive.
Once you get to the point where the dog calms down when you have this particular visitor, have your visitor slowly get to know your dog. Start by having your friend pet the dog. When petting your dog, be sure to keep your hand level with the dog's nose or lower, any higher and they may feel threatened and become aggressive. These should start out as gentle petting strokes and as the dog becomes more comfortable with your visitor, they can start giving commands and rewarding with treats. Repeat for any other friends or visitors and you will find that the dog will eventually come around.
The important things to remember:
medium-high pitched for rewarding coupled with treats
stern/low voice for 'bad dog' routine
never cower in fear from the dog
Hopefully some of these suggestions will work. If you have done all of the above, your dog is likely un-trainable via at home methods. At this point, you may want to think about putting your dog up for adoption by a rescue group. It will be easier to do this than to put it down and give a rescue group an opportunity to train and place the dog in a more suitable environment. It may be hard, but it may be the best and healthiest option for both you and more importantly your dog.