I moved all of my friend's Facebook data into MonicaApp [1] [2] (open source friends crm, you can self-host if you want, I pay to support the dev). I get reminders for any events per-relationship, and there's a reminders API [3].

[1] https://www.monicahq.com/

[2] https://github.com/monicahq/monica/

[3] https://www.monicahq.com/api/reminders