1)
Join Steam Beta in advance.

First, the host player should let the Steam client detect the number of controllers to play with.


2)
Then set the options for the host and clients in [Steam] > [Settings] > [Remote Play] Tag.
These settings affect the quality of your streaming play.

I recommend the host to check [Change desktop resolution to match streaming client] for comfortable multiplayer.
.

3)
And the host should check [PlayStation Configuration Support], [Xbox Configuration Support], [Switch Pro Configuration Support] and [Generic Gamepad Configuration Support] in Controller Settings from [Steam] > [Controller] Tag or Big Picture Mode.
This will somehow prevent problems that the client-side controllers are not recognized.
.

4)
Then follow the normal procedure to launch any of your local multiplayer games.
And invite your friends who also join Steam Beta from your Friends list in the Steam Overlay, select Remote Play Together.


But unfortunately, friends are priceless.