My 2 daughters have the same Apple ID so they can’t call each other and they get both text. How can I fix this ?

Give one of them a different Apple ID. Then have their Apple IDs linked to yours using Family Sharing. Two people should NEVER share an Apple ID. It leads to nothing but problems, as you are discovering. See-->Family Sharing - Apple Support. And if they are minors also see-->Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

You need to get them their own separate Apple ID’s. You can do this for children that are under 13 when you use Family Sharing. I recommend that you set up and use Family Sharing. It will make things much easier now and down the road.

Family Sharing - Apple

Set up Family Sharing - Apple Support