I just wanted to pop in here, and say this is something that I have struggled with at times as well.
In my case, it was whether to cull them for the table, which makes it even harder.
But as another member pointed out, as long as you follow through to the end, whether that is keeping them all their life, putting them in a cooking pot, or selling them, then you have not given up, and have fulfilled your duty to them.
The only time you would let them down, would be if you (not you personally) neglected them, and left them all alone with out what they need.
So if selling them is the best way to keep everyone happy, (and if they are fighting all the time, neither them or you are happy) then there is nothing at all to feel guilty about, and you are taking full responsibility for them while you can.
