I have one Xbox one x. I have two controllers. I want to simultaneously play on my iPad and...

Hi, I hope you're doing great out there. I am an Independent advisor and I am here to help you in regard to your concern.

You can only be signed in on one device at a time. This means that if you will be playing on both devices at the same time, one device should be signed in on a different account.

Your understanding is correct. It splits Player 1 so that it is controlled by two controllers.. or as you put it links two controllers so that they were as one. In my case, I have two kids. Rather than ask my kids to pass over the controller I just let
them think they are controlling the character. But I assist them when all else fails. Or I let my two children play as one because I have many single player games in which it could avoid having them fight.

I also left the controller connected to Xbox but it's too far away. I have my Xbox One X downstairs and I have a Windows 10 PC upstairs. The two controllers disconnect due to the long distance away.

I successfully connected my controllers to my Windows 10 PC in copilot mode (to play Windows 10 games). I also successfully connected my controllers to Xbox One X in copilot mode but in direct sync to the console. However, I am not successful in linking
the two controllers in copilot when streaming Xbox One X to my Windows 10 PC. In the last case, my controllers are physically connected to the Windows 10 PC while it is streaming the Xbox One X. The controllers are connected in regular fashion (i.e. they
do work as player 1 + Player 2) in this streaming mode but in configuring for copilot mode or accessories, the streaming does not recognize any controllers despite the controllers functioning as two players. I have tried using USB too to ensure that it's
not the wireless adapter issue. Same result. It might be a situation that isn't anticipated. Nonetheless an issue I stumbled upon as I am avoiding having to relocate my console from downstairs to upstairs. That may be the case if I don't hear any suggestions.

I am not trying to connect the two controllers simultaneously on Windows 10 PC and Xbox One X. Just the copilot mode on Windows 10 PC in streaming Xbox console.

Yes we all are playing on xbox one consoles. I have the One X, two of my friends have the S and two have the first gen Xbox one. I was able to play with two of my friends that had the first gen and the S

We have two iPads, in our house, but I definitely want one of these babies.

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Pro version, for me.

I don't believe such a set of headphones exist, but you could get a pair that allow both wired and Bluetooth connections simultaneously and have one connected to the ipad for fortnite or any other game and the other to another device running the Xbox app.
I do not believe there is any way of achieve a mixer between the two on one device unless it is supported somewhere in your devices software settings.