Yes, for nests it’s best to only have one entrance, although if there were two, the hog may well block the second – that is, if it was good at making nests! But they can block one entrance with their spines so it’s safer really for nesting to only have one entrance. When they make hibernacula (if it is well made), there is a central round hog sized chamber for them to curl up in the middle. The entrance ‘tunnel’ is pretty much closed behind them, probably to minimise draughts.
But, for feeding of course that could be inconvenient if a second hog got trapped in a feeding box, with the other hog blocking one exit, so a second exit could be useful.
Yes, hogs do like to keep us guessing! Glad to hear the hoglets are putting on weight. Hoglets are often last to hibernate, so they have a bit of time yet if they choose to stay a bit longer and put on more weight. Some hoglets, of course, choose not to hibernate at all.