I dont pretend to be an expert, but what i have been told is that,
some jills will eat others kits, if kept in close quarters / jelousy.
As they have been housed together for a few years you should be fine, but theres always a chance of the inevitable.
If i have a litter i plan to house my 2 jills together as they have lived together since berth, so they should be ok together at birth.