Pre#1) Although they've been happy for a few years together it is in their best interest to be living in separate tanks.

#1) I don't believe you have anything to worry about in regards to handling your snake. Ball Pythons are very timid snakes.

#2) Although I have yet to hear anyone contract salmonela from a bp, the risk is there...regardless you should wash your hands after handling.

#3) They will not smash out of the tank to find the baby. The baby does not smell like food. Bps are imprint feeders and therefore will only indentify the rodents you feed them as food. Do not leave the baby with the snakes out unattened I think thats an obvious one but hey i'll throw it out there.

#4) Nope