Multiple Xboxes, network issues

Hello all,

I am the oldest of 4 children, who all live in the same home. We have 4 Xbox consoles; an Xbox Series X, an Xbox Series S, an Xbox One S, and an Xbox One. This is because we all play to some extent, and frequently play together.

Recently, I've been having various network problems, mostly related to ports and NAT type.

The first issue is that I, on my Series X, will frequently get Moderate NAT type in game, even if I am the only one on the network. This is a problem because a lot of my friends have poor connections often resulting in Strict NAT, Moderate on a good day. I would like to get Open NAT for myself, so that I can host and thus resolve things. Problem is I can't simply forward ports because of the risks it entails. UPnP is also out for the same reason. I have considered DMZing my Xbox specifically, but my concern is what if the OTHER Xboxes start having the same problem. I have read about the conflicts DMZ can cause with multiple Xboxes. Another option on the table is port TRIGGERING, as opposed to forwarding. To my understanding this would allow any XBOXES on the network to connect to anything I "forward" just fine, while leaving the firewall intact for the rest of the network.

I should probably pause here and explain that I am relatively new to this particular area of networking. I've been researching this for a while and all the terms are frankly starting to make my head spin. So if any of this is unclear, that's probably why.

The second issue I've been having happened today, actually. My sister was on her Series S trying to play with my friends and I, but she couldn't connect to the Xbox party we were in. It got stuck on connecting, which immediately made me suspect a port related issue. I eventually solved that by having her make a new party on her Xbox, but the whole situation really doesn't make sense to me. How is it that only one Xbox can successfully connect, but when the ORDER is changed it works fine? And what router settings could I change that might fix connections once and for all?

My only criteria is that the only exposed/at risk network devices are the Xbox consoles themselves. The rest of the network can't be exposed to anything.

TYIA, I am ready to listen to advice on this and I will be here if there are any questions.