Minecraft- Cant join my friends(Not on Beta)

Is it possible that your friends signed up for the Minecraft Beta in the Insider App?

If that's the case, your friends either need to leave the Minecraft Beta and play on the "regular" version, or you'll have to install the Xbox Insider App, and join the Minecraft Beta as well.

Is it possible that you have joined the Minecraft Insider Beta program, and you have a newer Minecraft Beta version than your friends?

Yes i did join the minecraft beta and i notice i couldn’t join my friends so i unsubscribed to the beta unistalled minecraft then when i tried installing it back i had issues which leads me to where im at now

Your son is playing on the official release channel for Minecraft. His 1.12 version is currently the latest official version, whereas his friends have joined the Insider Program and are playing a beta test version of Minecraft.

His friends can either un-enroll from the Beta Insider Program, or you son can try to join the Insider Program and update his Minecraft to a beta version.

Be aware however, that beta version still contain untested parts, and the game can crash, malfunction and in turn destroy worlds if an error occurs.

If your son is still willing to test the Beta, he can download the free Insider app from the store, and join the Minecraft Beta.

Then he'll have to download/update his Minecraft to the newer beta version.

Your friend may indeed have a beta version of Minecraft. If that is the case, they will not have access to Realms and will not be able to join non-beta players while previewing the beta.