Oh my god, I dont say this to be mean but your mom is not nice to your dog
!
If I were you I would not let her go near him without you watching, and if he does something wrong and she's going to hurt him then go into the ''fight'' and try to stop her !
Where I live this is animal abuse and here the dog would propably be taken of a person who does this (its illegal to hurt any animal in some way, except accidents ofcourse).
My Fido is not allowed around my mom without me watching cause she gives him constantly something unhealthy to eat and he's too fat I'm trying to make him loose weight, I just have Fido all the time with me when I'm around my mom.
Your dog propably does this cause he's scared ! IF you two (everyone around the house) would use positive training on him this would propably stop.
Try to encourage him all the time when he's just doing nothing, just maybe laying on the floor chilling, then say something nice to him and pet him.
If Fido peed on the floor when he was younger the only thing that worked (i've babysitt many dogs and I worked on an animal clinic so I know much about this stuff) was to be positive, encourage when the dogs behaving well, and when he pees inside or poops then just say ''NO, bad dog!'' and let him go outside immediately undil he finishes if he wasnt done yet.
If 1 dog is allowed in the couch, all have to be allowed ! its impossible to allow 1 but not the other , then its just constant whining and the other dog feels like he's left behind.