I had the same experience. That bit about two people being able to take a guild hall was exciting to me because I've had an unfinished guild hall mission sitting there for a couple years. I immediately switched to trying to claim the new one.
We tried with 2. Tried again with 3 and at least got to the 4th boss. Hopefully we'll be able to pull it off with our full 5 person membership. But doing it with 2 is unrealistic unless those 2 have high DPS and execute everything almost perfectly. I think 3 is a more realistic minimum number.
If you want some help let me know. I'd be happy to assist.