1. The Tularean Caves, as near as I can see, were blocked by BDJ because he dropped the Loren Steele quest and there was no reason to enter them. I guess he didn't want anyone trying to rescue Steele. I'm second gueeing him here as I really don't know why he did that.2. This is a bug that was never fixed and the only way to fix it is to use an editor. Since there is no Dark Path (see answer 3 below). I don;t think he can even learn Drk magic, but maybe he can.
3. Once you complete the Soul Jar Quest, Sir Canegham will tell you that we are now allied with Archibald and that you should see Maximus in the Pit for a quest. This is the one I mentioned in my last post to you and it is really tough for a level 1 party. I hope you trained up for it as you will be fighting groups of 10-20 devils (in the first house), and then archangels (these will dispel any buffs you have on your party), and assorted golems in the temple. Those blue dots you saw will become enemies to fight in this quest as it is the same temple.
4. BTW did you clear out Morcarak's Cave on Emerald Island and the White Cliff Caves in Harmondale . . some really nice artifacts in there.