I would say forgoing the biopsy and just neutering him and doing the scrotal sac removal at that time. It needs to be done and putting him thru 2 surgeries that more than likely will have the same outcome with a dog that age isn't worth the risk. I would definately have bloodwork done prior to the surgery though to make sure he's healthy enough to go thru it. Until then you can try putting an athletic supporter on him to stop him from licking until you an get him in.
Let me know if you have any other questions
Good Luck &
Best Fishes