Can I backup 2 iPhones to 1 mac

Yes, you should be able to. When you plug the iPhone in, just make sure that you select the correct device. If you are only plugging in one at a time, it should be easy. When you back them up, it identifies the phone that is getting backed up, so there won't be a mixup. Back up and restore your iPhone or iPad on Mac or iCloud - Apple Support

I also rename my phones something like iphone1 and iphone2 so I know which backup is which.

Good call.