Why would you not just bag both snakes, sterilize both tanks, put the baby in the 30 and the big guy in the 100 ?
Both of those tanks are much to huge for a ball, but at least that makes more sense than putting them together in the same tank, no matter how big it is. That is just asking for something to go wrong.
By the way, welcome to BP.net! We hope you will stay and learn from us, we'd love to see pictures of your snakes some time. Most of us here got into snakes under less than ideal circumstances, so we can sympathize with you, and of course we are happy to answer any questions you may have and help you become a better owner. I've been here for 3 years myself, and I still learn something new about every week.
Gale