I think there is something wrong with these iPads from your cellular carrier.
I have only had one heat issue with my very first iPad 1 over 5 years, ago.
It was a heat issue very similar to yours, now, and my iPad got soo hot from charging and the charger, itself was just as hot and it put a wide, full length heat crack in my iPad 1 screen.
Instead of bringing these iPad Minis back to your cellular carriier, I would find where your nearest Apple Store is and bring them there to see if Apple directly will give you a better replacement/refurb iPad Mini.
It is possible that your cellular carrier maybe carrying a defective batch of iPads or a bad batch of refurbished iPad models that they maybe selling on spec or for promotion.
I would just deal with Apple with your iPad Mini issue.
If an Apple Store is too far away from where you live, you can contact Apple directly at 1-800-MYAPPLE and ask for sales or customer support service and calmly explain the heat issues you are having with both the iPad Minis and see if Apple, directly, will offer you another free replacement iPad.
If you have to, if no joy from the first Apple employee you speak to, calmly ask for the next higher level customer service employee and calmly re-explain your iPad Mini issues to that new Apple customer employee.
If you need to, keep moving up the Apple customer service chain until both you and Apple reach an amicable resoultion/solution to your iPad Mini issues.
Good Luck!