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As I understand, as of iOS 14 the messaging filtering for unknown senders works for both iMessages and regular text messages. However, while it filters messages into their own section in the Messages it doesn't seem to do anything in relation to notifications for those messages as the notifications still come in for them.

This is rather odd behavior given that the previous option that was there just for iMessages would actually silence the notifications for those as well. Also, the very similar unknown caller option also silences them.
Unfortunately the toggle ONLY filters spam SMS in India (for reasons). Everywhere else it only applies to iMessage. Like I said earlier, I'm relying on an app to do the SMS filtering for me. Annoying you need an app, but it works so is worth it for me. Luckily ALL of my spam texts contain the word "Ronald" which isn't my name, but they seem to think it is.

I don't currently use the filter all unknown option in that app as filtering for the word "Ronald" works for now. Eventually I may need to enable the "all unknown" filter in the spam filter app as well.
 
Given that is a close family member and seems to be a "hacker." I'd make sure you change all your passwords and begin using two factor authentication as well. Don't forget to change your wifi password.

Given she knows the family well, she will be in a prime position to guess simple passwords like kid's names, birthdays, pet names etc. She will also be well positioned to be able to sweet talk your acquaintances into giving up your new numbers.

Also, make sure you don't put your new phone numbers into social media services like Facebook.
Yes 1Password the free version is key. Random password only.
 
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