Regit has given you spot on advice in every post. You should print the whole thread and take it to your friend for future reference! You absolutely
must separate them, or you can never be sure which one/s are regurgitating. Regurges are very dangrous to young snakes, and it doesn't sound like it's happened just the once

I hope there is some improvement soon.
Just a thought - if the plan is to divide the viv into three, you need to keep in mind that the temps have to be correct in all three sections, i.e. they all must have a cool (mid-high 70s) area and a warm (mid-high 80s) area. This could be tricky unless your friend can afford to replace the presumably square-ish shaped heat mat with a 'strip' one that is large enough to run along the entire length of the viv.
Also, each snake needs at least two hiding spots, one in the cool area and one in the warm area, so unless there already are 6 hides, that's something else that needs to be purchased!!
Lastly, as you will most likely need to use a non-toxic sealant to fix the dividers in place, the snakes will require somewhere else to live temporarily. Their stress levels must be kept as low as possible considering how ill they potentially are. But you also can't risk them inhaling, injesting or sticking to the sealant.
If this is the method your friend chooses, plan carefully. There are loads of people on the forum that have done this, and can give you loads of tips.
Good luck!