When I have had a cockerel running with my girls I noticed that the two ex-barns are the ones who lose the most condition from mating and even now, a couple of months after the last cockerel went, one of the girls has not refeathered as well as the others as a result. You will need to keep a close eye that he doesn't favour just one of them as although a strong purebreed would be able to cope with this an ex-bat may find it too stressful and will suffer more. Although a saddle would solve this problem in terms of feather loss if they still have weak bones there could be more serious damage.
I love having a cockerel in with the girls and don't by any means think I am trying to put you off as I think if they are strong enough to go ahead and try as they will actually prefer having him around
We have forgot to tell you we need pics of all your little feathered ones - 'tis the law on here