The Scenario Special Rules are:
- Except for the Justicar, all Angels cannot be moved, activated, or attacked by any means, but they count towards the maximum of two Characters per Space limit.
So, answering you questions:
The mission says that the angels cannot be attacked or moved.
Can they still attack? Do they have guard reactions?
No, the Angels (except for the Justicar) cannot attack. No, they do not have Guard Reactions (except for the Justicar).
If I pick up a card/ability that says I can make a monster attack, can I use them to attack someone?
No, if you pick up a card or ability that says that you can make a monster attack, you cannot use one of the Angels (except the Justicar) to attack a Hero.
Also the sacrificial pit says you get 3 wounds when you enter it.
Does that include the portal?
When you enter the sacrificial Chamber, even if you enter by using one of the portals, you take 3 Wounds. But remember that it only happens once per activation.
Is there any reason to use walk in from there other than go through the other portal next to the judge?
The portals are laid out in this manner to avoid player positioning from blocking passage for other players.