I'd start with NILF training (nothing in life is free) and a quick search on here will provide tons of info. Under the current circumstances I would only pet him, if I was your mom, when he was standing up, not when he came over to her, rather only when she called him to her. I would also pet him under his chin and not on the top of his head initailly. Ben loves to be petted, but only for a certain amount of time, then he's had enough...perhaps this is part of it too but there isn't enough details. A video would be helpful if you could record it without risk of a bite, and another option may be to contact a behaviourist who uses positive reinforcement.