Ready Set Bet is pretty fun yeah, we like it quite a bit. We normally have one person manage rolling the dice and moving the pieces, cause it feels more fun than using the app, but that does go a bit slower which makes it a bit more tactical and less frantic (which might not be what you want from a horse racing game).
The only other party game I've played that supports up to 9 players is Bug in a Rug. I quite like it, and you can just print out the sheets and use pencil and paper to play it. We actually played a 9-player game of that on Christmas after our big family dinner, and it was pretty fun.
ImaginIff goes up to 8, but when I tried it with my friends they weren't really into it. Your neighbors might think it's fun though. Pretty simple game and not too stressful I think.
Just One is really fun and easy to learn, but it only goes up to 7 I believe. A good word game as well, my grandma always likes word games. Would highly recommend it.
Mysterium is also pretty fun and goes up to 7, but it does take a bit more time to set up and teach. Can be pretty fun, but it does involve lots of looking at art cards and my grandmother reads too much into the details so she isn't that good. If you play as the ghost you could learn to work around that and give them cards based on how they play though.
There's also Codenames, I've played Codenames Pictures and liked it but scaling to 8 is really the max I would go I think.
King's Dilemma is a really fun legacy game, we found some adjustments to play with up to 7 players. It works pretty well, although 6 might be better. A nice story-based game as well, where your choices impact the story over the course of around 15 sessions. We're like 6 games in and it's been really fun. It does have a couple gruesome descriptions though, but it hasn't been too much of an issue for us.