Worst case scenario, you risk the life of the female carrying the litter.

Often the young Mother isn't very good at doing her job & rejects a litter.

Sometimes nothing at all that you may visually notice goes wrong but physically you are putting a heck of a strain on their system. You won't get the best production if you work with animals not quite ready. Back to back breeding will wear them down even more. It sounds as though you were going to breed them up to build up breeding stock as your need is higher than what you can cover right now.

You may need to continue your current method of feeders to a point as you grow your home production & then gradually move yourself over to your own.

Good luck with it all.