1 find out what the load rating is on the beams. Need specifics. Tji?

2 what kind of pipe? Whats it for? Your only solution is to dig it up. Rent a track hoe mini ex to get close. Then hand dig the rest.

3. No code violation. No issue. Offer to remove the deck if they balk.

4. Find mysterious hanger. Buy hanger. Swing hammer.