I have 5 M5 Decos for my 2 story 2500 sq ft house.  I have one Deco in the center of the house connected to the modem.  All other Decos connect wirelessly to the main Deco.  I got more Decos than necessary because I wanted coverage to extend out into my backyard where I have multiple cameras covering my chicken coop.  We had around 25 devices connected at any one time.  But recently some of our devices can't connect.  It seems like we are capped at only 18 devices now.  In order to connect an unconnected device, I have to disconnect one of the existing connected devices.  This does not seem right.  I should be able to connect many more devices than just 18.  The devices that can't connect are our iPhones, which disconnect upon leaving the house, but won't reconnect when we get back home.  I updated the firmware but this did not help.  I also turned on the guest network, but nothing wants to connect to it.  I'm not sure how to force that or if it will make any difference.  Any suggestions?

The problem could be that we have too many devices connected, or it could have something to do with our iPhones.  Are there any settings that we need to change on the iPhones to get them to connect?

Also, if the problem is the number of devices connected, would adding more Decos allow me to add more devices?

Thanks.