Hi Chelsea Girl
Sounds like your hog houses got a definite seal of approval! It’s really important to provide potential nesting material, as you did, to encourage them to use houses more quickly.
It isn’t unusual for hoglets to share when they are small, but they tend to reduce to one per house when they get bigger. However, hogs seem to like to keep us guessing and I had two huge male hogs share for a short while! That is more unusual, though.
The adult hog next door may or may not be mother of the hoglets. But there comes a time when a mother hog leaves her young ones to go it alone so that she can concentrate on putting on weight for herself, ready for hibernation. From birth to independence the young ones grow a huge amount and it takes a lot from Mother hog to rear them successfully. So she has a lot of condition to make up.
I hope the hog and hoglets continue to do well. Good luck and happy hog watching!