Urgently Looking for an App to Help My Parents with Reminders

G’day everyone, Hope you’re all doing well!

I’m searching for a free or affordable app (or software) that works with multiple iPhones—and maybe an Android—that can send reminders via app notifications, email, or something similar directly to individual devices.

Why I need this: My parents are getting older and have started forgetting important tasks, like paying bills. I’d like to set up a simple, separate system on their phones that reminds them of upcoming bills. I don’t want to use Google Calendar since they already use it for other things, and adding more would just clutter it.

The idea is to set it up once on their iphones and let it run without needing constant updates from me.

If anyone has suggestions, I’d really appreciate it! Thanks in advance, and I hope you have a great rest of January!

Cheers!