Double NAT on Airport Time Capsule connected to Airport Extreme connected to Solis Cellular Router

I do not have internet at home as a land line. So I had to buy a Solis Cellular Router which connects to any cell tower [or my personal hotspot on iphone] and these both can provide internet. I want to have a home network so I can do backups on Time Machine. I found a way to do this by connecting an Airport Extreme to join the Solis Network [or hotspot] and then the Airport Extreme is connected to a Time Capsule via ethernet so that I can create a wireless network on the Airport Time Capsule. This is done because the Time Capsule won't do this when I use a hotspot on my phone as the internet [i.e. the Time Capsule cannot join the hotspot and provide internet to all devices]. So the Airport extreme is in bridge mode and the Time Capsule is DCHP and NAT. However there is a yellow light and double NAT error. Everything works and I am able to do backups, connect to multiple devices, etc. If I bridge mode it, only one device will connect to the Time Capsule. How can I set it up so that there is no Double NAT? No yellow light. Maybe it does not matter but I thought I would ask.

Diagram of setup. Solis cellular router/personal hotspot iPhone-------[wireless signal]------Airport Extreme in Bridge Mode and joins wireless network/NOT extend wireless network---------[ethernet]------2 TB Time Capsule in DCHP and NAT------[Wireless 2G and 5G network in house]----4 clients