...it needs to support Sky's MER
I know you are only repeating what you have read, but it’s DHCP 60/61, not MER. Yes even Sky refer to it as MER on the Sky Hub status page, but they are also technically wrong.
Ok guys, strange...
I managed to get my sky setup through the TaoTronics only, disabled WiFi on the modem, when I done this, booted up my Xbox and double Nat was back
I then done “test Nat type” and once completed its back to wired and on Nat type, open.
You get double NAT because you have the mesh doing NAT as well as the router, the router won't not do NAT, presumably you've configured the router to, which is why you have double NAT.
So far you've purchased a 3 node set-up that can't act as a router with your chosen ISP and now ordered a router that won't work with Q mini's, when in all likelihood all you actually needed was a free booster from Sky. Buying things when you have no clue what the implications are generally ends up being expensive and generating other issues. Cabling Xbox to a node still means that connection has to go via wireless back to the primary node (unless it has a dedicated wired backhaul as well, in which case why not just use a switch in the first place?
1. Can you run a cable here or not? If so do it.
2. Have you asked Sky for a booster?
3. If you insist on keeping your new mesh system, you need to set it up properly, not in router mode or you will get double NAT.
Whatever you do, please stop randomly buying things without doing any reading up, you're creating more issues than you're solving and spending money for the sake of it without any real benefit.