I agree with Deuce! Go see Marco and see if Jackson and him get along. I would also ask to see his veterinary history. If Marco is as well taken care of as you think, the family will have a folder for him. At least that's what I do with every receipt from the vet.
I keep it all together so I know exactly when Kaji went to the vet and what did they do. If everything checks out, OH MY GOD! You'll have 2 babies.
You may also want to leave your wallet at home. Make it clear this is only a first visit to see if the boys get along.