If they were up and standing as much as you say, that alone should be enough to ask the FA to intervene. I know that the seatbelt sign off means it's presumed to be safe to get up, but it doesn't mean passengers can turn the airplane into their own personal lounge-fest.

No way would have I put up with that for even 30 minutes. All you have to do is tell the FA that you feel there is a safety risk by having people standing around you in the aisle. After all, the number one responsibility of the FA is to ensure passenger safety.....