Nintendo Switch

I have my kids' switches all set up in the family group and have the parental control app on my phone (and tablet - in case my husband needs to access it when I'm out of the house). They like playing locally together (on their separate systems), and I want to keep this, but... I don't want them playing with strangers online.

Is there a way I can lock it down to where they can only play with their friends and no new people can send them a request (and they can't send an outbound request)?

This all got brought back to the forefront when my 7 year old (who is developmentally disabled) was playing with a stranger on Minecraft Dungeons last night.

I also tried to change Microsoft family settings and kept getting errors on their end. Website gave me a generic "we're having issues loading this page" error and I couldn't seem to find what I needed in their app.

I've tried searching online without luck, and when I try to change settings (semi blindly) I end up taking away their ability to play with each other.

TL;DR I'm wanting to limit their online interactions with just each other until they're older/developmentally ready. Looking for a way to block all incoming friend requests or a way to just limit online co-op play with just people on their friends list. Switch and/or Microsoft settings that need to be changed will be appreciated.