It says 2-8 as the party limit, I really don't think any party of 2 could finish that quest without having some massive supply of consumables. I'd suggest it to be 3 or 4 to 8.

It's available to groups of two if they want to try it. Of course, any adventurer with some common sense would realize it would be dangerous to do anything with just one other person. Adventure at your own risk.

Other quests have minimum party sizes over 2 though.

If two people want to try it, they should be allowed to, IMO!

core If two people want to try it, they should be allowed to, IMO!

I would hope that if a two-man assault of the fort was attempted that the players involved were either veterans or EfU or players who don't mind losing a character to overwhelmingly insane odds against them.

Or ninjas.