How can you manage relationships between the various school actors?

Well this can go many ways.

-if you mean boy/girl crushes, you can't help someone who has a crush, but make sure the roles they are given don't interact wit one another and there aren't personal scenes with them.

-if you mean like best friends, they will most likely chat whenever they get the chance, so try to keep them busy, but encourage them practicing together. It is good to get encouragement from someone you know and trust

- As for hating, you can't do much with that. All you can do is make the most of it, for example, in the play, if two characters are supposed to constantly argue, then maybe consider those two for that. NEVER EVER give one a position where in the play they rule over the other one(one is a king and the other must serve him) that will create serious real life drama

The best thing to do is to make the most of the talented characters you are given.

And remember...

True actors will get over their real life conflicts and leave them behind when they go on stage to perform. Bad actors will not play their part well because they are too distracted.