Neat idea but getting a 5G GL inet router would probably be more robust. Built in tailscale and wireguard so you don’t have to worry about this. Best thing about GL inet routers are the IMEI cloning. It’s pretty popular for wireless ISP like T-Mobile and Verizon 5G home internet.
While I have no experience of their 5G routers specifically, based on my experiences with other GL.iNet routers and the TG-Link I have, I don't disagree. The Deco they have has the benefit of easy mesh wifi setup with fast roaming, but the easier access and configurability of GL.iNet are generally nice, and they're fairly affordable.
Since you have tailscale, and assuming your parents don’t do anything fancy, you can always double NAT. It especially doesn’t matter since you’re on CGNAT. Use the gl inet router as the primary and attach a mesh router behind it. You’ll be able to configure the secondary router through the primary.