The only way to get max HP on Level-ups is by Saving beforehand, Reloading, and trying again. And hey, good luck getting Jaheira to roll her maximum. She's great in BG2, but.....not here, baby.
You're already IN the Gnoll Fortress.....there is no "interior," sorry. The movie that plays when you entered the map area shows you pretty much the whole thing. Note: The Gnoll Stronghold has VERY poor visibility: There are 2 little areas on the roof that you simply
cannot see until you're right next to them. Dynaheir is in a similar location: I can guarantee that you're already walked right past her about 3 or 4 times without seeing her. Get happy with that mouse cursor--if it says you can walk there, WALK THERE. Don't be satisfied by just
looking.
Chapter 13 of my site may prove informative as well. It's not just for BG2, you know.