Last night the cats stayed out till dawn. I called them every hour but they were not bothered. The two indoor cats are fine, they love being out now. They sit on garden walls and seem to stick together. They follow the outdoor cat around and the dynamic between them all has really settled down. They are being very loving when they are in. Lots of purring and cheek rubbing. They seem to be staying round the back of the house and garden, keeping away from the road.
If I can find them in all the foliage I will try and post some photos of them.