Other than the tumors in his mouth (That I personally would get taken care of quickly), his other symptoms sound like
aging arthritis......Your Vet can prescribe
Anti- inflammatories that will work wonders to ease his pain......
There is no reason for him to suffer like this as the meds from your Vet will give him a new lease on life.....Please, get him there as soon as you can....Let us know how he's doing....