This sounds like the batteries are degrading to the point of swelling and causing your screens to be pushed outwards. I would recommend stop using these phones and either take them to an Apple Store or authorised repairer to check. They will put the phones through a diagnostic test to determine the condition of the battery. If the battery has swollen, then they will have to send the phones away to get the battery swapped, (normally done in store) in case the battery explodes and sends its contents all over the place. There was an iPhone 5 battery replacement program some time ago, and if you put your serial number in and said it was eligible you could go in and have it swapped for free. I don't know if this is still running, or has now expired. Wouldn't hurt to check though.