The only time I hold 2+ snakes at a time, is when they're the same species & approximately the same size... like when I was holding 4 of my baby BPs the other day, while moving them onto the bed for a few photos (and to clean their tubs). I wouldn't hold my hognose and a full-grown BP near each other, though, so I'd think the same would apply to a BP and young boa. Like the others said, a fight/bite is unlikely but not worth the risk!