Here look at it like this they may keep eating and will be fine in that enclosure. However if they are not ok you have multiple reasons why they might have gone off feeding, is the cage to big or is it because they are stressed due to being housed togeather or a combination of the two. You can throw illness into the mix and if one of them gets sick you can pretty much count on them both getting it because they are housed togeather. My point is if any of this happens your solution is to separate them and move them into smaller inclosure's and go from there. So weather you wait for it to happen or you are proactive and do it so it will not happen the outcome will end up being the same.
I can't even tell you how much money I have waisted keeping my snakes trying something and finding out it sucks or beginner mistakes. The point is I learned you don't have to make it fancy to keep them correctly a thermostat, two steralite tubs and small UTH and you are set. Look giving up one to your brother isn't going to fix your problems here you need to get your husbandry right and we will help you do that but that tank is too big and you should house them in diffrent enclosures.
Chuck