A long time ago I received the quest to trap someone and slay them. I just picked up a Dark Brotherhood Iniateband took him there. I can't figure out what to do next. Activating the pillar doesn't seem to do anything. I also tried making him wait next to it and then activatie it, but it does nothing.

I don't have the book anymore and don't recall receiving a blade of sacrifice.

I have another quest to lead someone to the abandoned house but when I get there nothing happens.

I'm not sure how to proceed.

Are you level 30 yet (I think that's the minimum level requirement)?

I'm level 60

Ask your follower to do something, then select the altar.

I did ask my follower, I'm going to try with a different one.

I killed all the cultists and have like 7 of the Blades of Sacrifice, but I beileve there's an opttion to talk to them as well. Maybe the follower you had wasn't a true follower (ie one from a quest). I haven't done DB yet so IDK if "Dark Brotherhood Iniateband" is a normal type follower.

That happened to me before with the DB assassin initiate. I switched her out for the Headman of Solitude and he worked.