A baby bp is just going to be super stressed by living with a more grown bp. They'll be competing for the same space, heat, and hides- its just better to house them seperately. I know you probably don't want to spend the extra money on another setup, but theres inexpensive ways to do it, such as a rubbermaid enclosure. Doesn't look at nice as a terrarium, but very functional and easy to maintain.

You will have happier snakes if they are housed seperately.