Energy difference or what..?

It could be the other dogs setting your dog off. A fast paced power-walk may set off the predator instinct in a dog. If this is the case, your dog may be trying to protect you and your mom in his own way. Try slowing down for your walk, if your mom will let you. You need to reure your dog that the other dog will not hurt you and can be ignored, unfortunately that is not happening with your mom along on the walk. Can you stop and let her continue on? Good luck