Verizon to T-Mobile Conversion

In May I purchased new S6 edge for my wife outright to keep Verizon Unlimited data. In August we switched to T-mobile due to the need to have Wi-Fi Calling to get any.... yes any.... service at my new house. The phones functionality is at best limping along at this time we have done several factory resets. All APN settings have been verified by T-Mobile. The phone is just handicapped now and worst of all No Wi-Fi calling due to non T-mobile rom. My son has a Nexus 5 and I have a Nexus 6 so I just threw stock t-mobile roms on them and all is well everything works as perfect as one would expect. These piece of **** branded garbage Samsung phones my wife loves leave me confused about what is possible.

Question 1: Can I flash a T-mobile Stock rom to a Verizon S6 edge or will it brick this thing?

Question 2: Does anyone know what benefit having 6 different model numbers for each of the carriers provided Samsung? There couldn't have been a cost savings! Making one phone that works on all carriers seems like the most cost effective option, hence the benefit of my 2 nexus devices.

Thanks in advance for any help guys.