Unable to connect

On Minecraft pocket on iPhones, my kids can't join any of my worlds. It says, "Unable to connect to world". I can usually join their worlds if we try a few times. Usually we need to power cycle our devices and force quit the app several times. We turn WiFi off and on etc.Sometimes signing out of our accounts and back in works. Usually that takes less than 15 minutes. I've tried all of these steps for over an hour. I've even changed to standard skins and lowered to 4 blocks simulation distance for the older device. We used to be able to play together on my worlds sometimes. This time, one of my sons was able to join me. Then, it took me about 30 minutes to get my other son to be able to join by doing all of the aforementioned steps. Then, I tried to invite my son that was previously able to join, and he got the same error. We all quit the app and relaunched and tried again, and nobody could join. I'm so very frustrated because we all love the game, but we can't even all join the same world on my account. Also, it bothers me that it takes up to 15 minutes to figure out how we can all play together every time we try to join one of their worlds. I have iPhone 11 Pro. They have iPhone 6 and iPhone SE (the iPhone 5 form factor iPhone SE). All on the current version. I worked at Apple for 8 years doing tech support in the 2010s, and I've never had this much trouble with my own devices. We're all on the same local WiFi.