Only can share one iPhone's location at a time from a shared Apple ID account with two different iPhones and phone #s?

Apple IDs are personal; they shouldn’t be shared any more than you would share a toothbrush. If you share an Apple ID with someone else many bad things will happen. Each user should have their own Apple ID, then you can create Family Sharing (it’s free)→What is Family Sharing? - Apple Support. That way you can share what you want to share and not share what you don’t want to share.

It is OK to share an Apple ID among devices used by one person, such as an iPhone, an iPad and a Mac; in fact, it is a very useful thing to do. But not between devices used by different people.

Here is Apple’s FAQ: https://appleid.apple.com/faq/#!&page=faq. See the 4th bullet item.

And here is Apple's expansion of what I've posted→Make sure that each family member has a unique Apple ID - Apple Support

What you are trying to do can be done. But not the way you are doing it. Set up one account as a Family Organizer, and create others to join it.

See Set up Family Sharing - Apple Support

This is quite simple: because of apple id's are personal and are not meant to be shared