It is possible that the chickens. or some of them might feed the need to peck the rabbits. We used to see the chickens gang up on one partiicular bird and peck its backside until it bled. Bit unpleasnt of them and we never knew quite why.
The only answer was to put some kind of tarry substance on the pecked chicken's backside in the hope that the other chickens would not like its taste very much and would therefore stop doing the pecking. It sometimes worked!
If the chickens decided to have a go at the rabbits it might be a real problem.
Les