Deleting Group Chat in iPhone Messages

Unfortunately, it is not possible to delete a group conversation if not all users in the group use iMessages. The best thing you can do is block your sister's husband, and delete the group conversation and start a new one without him.

You can find more information about group chats here:

Leave a group text message thread on your iPhone or iPad - Apple Support

You can find more information on how to block a number here:

Block phone numbers, contacts, and emails on your iPhone or iPad - Apple Support

"Deleting Group Chat in iPhone Messages: So I have a family group text with IPhone & Android users. My sister is getting a divorce but her husband is sending harassing messages in the family group chat. How can I delete the chat permanently?"

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Ridding of Messages Permanently:

Set Up Messages, then Reset the iPhone:

What you need to do is backup data, and then enable Messages in the message app. Once enabled, reset your iPhone to factor settings, and recover these messages.

1. Set up Messages on Mac - Apple Support
2. Use Messages on your Mac - Apple Support
3. Messages User Guide for Mac - Apple Support

Resetting to Factory Settings:

If you are so concerned, then reset you iPhone to factory settings, as if you were to sell it. Go here: What to do Before you Sell, Give Away, or Trade in your iPhone, iPad, or iPod touch - Apple Support. Perform as instructed there, including the backup creation and iCloud logout.