As mentioned a group text goes a long way to resolving your problem. I'm going to a bbq this arvo organised on whatsapp. But also your solution sounds like it's

As mentioned a group text goes a long way to resolving your problem. I'm going to a bbq this arvo organised on whatsapp. But also your solution sounds like it's trying to disrupt/recreate Apple/Google/MS calendar, not Facebook events. I'd probably be looking into CalDAV or similar to ensure interopability with whatever system your mates/users are already working with in their day-to-day .. And then sprinkling some sugar to kickstart a slow-shuffle to your side of the dance floor. Good luck!