If any of them are male hoglets from last year, they might disperse. But also as more people begin feeding again some of the others might go back to previous haunts.
Yes, it would be nice to have some spare houses, for prospective mother hogs, but you might also find that as the weather improves the hogs might move out of the hog boxes more. Some of them prefer to spend the days in the undergrowth when the weather is warmer. They would not normally continue to stay in their hibernation nests long term – apart from anything else, due to potential parasite problems. Hopefully you’ll get a chance to give the boxes a good clean out soon. It is still quite early.
Good luck and happy hog watching!