8 players is tough... We play quite some couch cooperative games, so here's some recommendations. None of them except a single party game for 8 at once though, I'm afraid.

• overcooked was already recommended. I second that. It's great. But man, it's intense, too... You can only play this with people who can laugh at themselves. I've heard purple say that this game might jeopardise friendships and I get it.
• lovers in a dangerous spacetime is a game I'm madly in love with. It's a coop roguelike which mixes space and lasers (which worked well for some of our kids) with pink rainbow unicorn aesthetics (which worked well for the other kids) and is just all around great fun to play.
• boomerang fu was already recommended. I like the design and the the music has some real bangers, but it's a competitive game which might lead to some conflict, depending on your group dynamics.
• unrailed cost us quite some hours as well. We really liked it, but imho it gets quite tough quite fast - we rarely got to the third of iirc ten biomes. Maybe it's because we always play it with our kids. Maybe we just suck at it. Despite this issue, we sunk quite some hours into it because it just still works well.
• Trine is three players coop only... It's a platformer. I didn't like the design so much, but my kids love it, so I guess that's still a good verdict.
• pixel cup soccer is our go-to soccer game. It's obviously a simple arcade game, but it's fun.
• Sonic All Stars Racing Transformed is our Not-Mario-Kart Kartracer and it works well. Not a fan of the tanks in there for a kid's game though.
• the Jack's party box games or whatever they're called are a kind of mixed bag, but drawful is great fun. It's also the only game on this list for 8 players. You draw stuff on a phone or a tablet and there's a well-working mechanic to make people guess what was drawn.
• while I haven't played it yet (waiting for a deal), Turtles: Shredder's Revenge is supposedly a great take on classic streets of rage style beat em ups.
• Rayman: Origins is a beautifully made and well designed platformer that can be played cooperatively with up to four people. True classic imho.
• for a quick party session, our kids love ultimate chicken horse where you build a level and then race through it. Tbh, for me it didn't really provide too much replayability, but hey, if the kids like it, who am I to judge?