Are these 5 horses or 5 ponies? It would be interesting to know their sizes and do they all get on without bickering?I have a herd of 5 that live on a yard with a double field shelter. Yard is 30x30ft, they have round bale of hay in feeder and self filling water trough, I poo pick daily and its much better then stabling works really well.
quarry conveyor mats
the yard I used to rent had a smooth concrete yard in the middle (it doesn't look like OP's is smooth) and it was lethal for barefoot horses when wet-about the only surface I've met which is worse for barefoot than shod animals. OP I have a similar sized yard I am using for a pole yard in the winter (not as big) and that is tarmacked. I will have a small area where they'll have hay which will be matted-I have these ultra heavy, non sloppy quarry conveyor mats which are great. I have young geldings so probably won't turn out together.
I find that outdoor rubber mats get slippery in frosty weather. The condensation on them freezes.