Just upgraded to series X but can't make it home xbox

Unfortunately there's not. As long as you're signed into your account, you can still access everything.

They must be a way, seems like a punishment if I upgrade a console but then can't use the services I am paying for

Customer support can’t offer additional switches. If you’ve made five home Xbox switches for the year and need assistance, select Help when you see the message Can’t make this your home Xbox. You may be eligible to receive an exception. If you aren't given a survey, you'll have to wait until the limit resets on its own.

Because my 2 kids now share ultimate game pass or whatever is called this really isn't much use.

When the older son had his xbox one the 2 boys could share the gold pass and ultimate pass etc but now he has upgraded to x series these features are no longer shared between the 2 kids.

All I want is what they had when they both had xbox ones is to hVe the same now one has upgraded to x series.

Not really...

Xbox Series X games / upgrades / updates has to be installed onto the Series X internal or expansion card SSD,

You can have Xbox One games on your external hard drive that will get an Series X upgrade but the games will need to be transferred to the Series X and then the Series X upgrade will need to be downloaded onto the Series X SSD,

As an example...

I have Marvel Avengers on my external hard drive that will get the Series X upgrade and I will transfer the game over to the Series X SSD ready to download and update the game to the Series X version when available.