Sorry to read about your fighting problem. I am afraid to say it, but I think you may need to separate them. Sometimes siblings can stay mates, but more often than not there is rivalry between them. If you can spend some time watching the group at the weekend, you will get a better idea of what's going on, who's picking on who and how bad the fighting is. I have several with nicks in the ears, this normally happens when out on free range, as I have to give mine separate aviaries. The maximum I can have in any one aviary is only two now, as that's how they paired up. I did have three in a aviary not so long ago but one died whilst out on free range.
I was really disappointed when mine had there first litter, as I thought they would all be one happy family. They all seemed to be getting along great, then one day things changed, no more happy families. This happened in about the same time scale as yours, the fights started, even though I had them in a big aviary. I didn't want to have to part with any, so I fast had to build new aviaries. Since then I've seen this happen many times. The father often really seems to look after the kids, then after a while they turn on him.
To help reduce the fights, put in plenty of tubes and other places where they can all get away from each other. Put in separate food bowls with the same food in, so the shyer ones can all get to some food. Having them neutered does calm them down but it won't stop the fighting altogether. Also, don't be surprised if you see the young males trying to challenge their father, or the mother having a go at her daughter. You could keep them all, but you may need to build or buy extra aviaries. Although this all depends on how much more room you have, and the additional time it takes supervising separate free range.
So stick with for a while, see if anyone else posts some ideas, and keep an eye on them if you can. You never know you might be lucky and things settle down again, and this was them just sorting out an order. Oh, if you do end up keeping them all the lads will need to be neutered when they're a bit older.