I have an iPhone 6 answers an iPad Air and it lets me join a Group FaceTime call but I can’t put my camera on

You need a newer phone. The 6 cannot include the camera in a group call.

Use Group FaceTime on your iPhone, iPad, and iPod touch - Apple Support

To use Group FaceTime video calls, you need an iPhone 6s or later, iPad Pro or later, iPad Air 2, or iPad Mini 4 with iOS 12.1. Earlier models of iPhone, iPad, and iPod touch that support iOS 12.1 can join Group FaceTime calls as audio participants.

~Lyssa