Can 2 phones share the same apple id?

Anything relying upon an Apple ID as a means of distinguishing between devices won't be able to tell the difference between the phones. The only way I know of is to turn off syncing to iCloud for the services that are causing problems. Of course that means cutting off the phone from everything else using that particular service.

Texts are special because they can be sent either via iCloud or as SMS over your cellular data plan. Since I don't have cell service on my iPhone (I use it as an iPod) and I receive about one text message per year, I am not the best to answer your questions about this. I would think in theory that a message sent as SMS would only appear on a phone with that destination number phone whereas ones sent by MMS would appear an all devices using a particular Apple ID. On the other hand maybe when you type in a number Apple is pulling the destinations off Contacts and saying, "Hey, that number should be sent to Apple ID XYZ wherever they are." That's not something I can test.

About iMessage and SMS/MMS - Apple Support

Yes, but remember that you are essentially making them identical as far as Apple's iCloud services and purchases are concerned. It shouldn't affect anything you set up with a cellular provider.

They will have separate phone services, but if you're using iCloud Photos and you take a photograph on one phone, it will appear on the other phone too.

You're welcome.