Limiting who can see which encounter map

First let me explain my set-up.

I'm just about to start a new homebrew campaign. We have a mixture of physical players and remote players. 1 lives in another town, the other 4 are local but only 2 will be consistently playing at my house due to not having a suitable computer (at least right now). The other 2 might drop in from time to time, 1 more than the other.

My DM server is on a stand alone computer with a 2K monitor. I also have another stand alone computer acting as the local client (for the local players) with a 1080p touchscreen monitor and a 55" 4K TV duplicating the touchscreen display. I normally move the local players tokens for them using the touchscreen, but I might try setting things up so that they can move the player token themselves instead.

I like to have most of my maps in 1080p for convenience, and the majority are limited to a single level. But I have a couple that are sets, for example a cave that leads into a temple, then the players eventually go through a hidden door and down a winding set of stairs in the temple to find the bosses cave complex and lair on a lower level. So it is conceivable for my players to be split up between the two levels as they explore.
With that in mind, I've figured out how to bounce between maps on the client computers, but to do this I have to share both the maps with all the clients which will kind of work. But it seems I can't choose which map a client sees from the DM computer, which means it's up to the players to coordinate which map is being displayed.
In the end what I'd really like to do is only share a map with anyone that is actively playing/moving on it so the other players won't always know what the split off player/group is doing or what's been discovered by them.

Is that even possible? If not, will FGU maybe have the capability? If it is somehow possible either in the current program or FGU I can see being able to take it up a notch from my current need too, like a trans-dimensional portal that takes each player to a different map when they enter it, etc.
I should mention, so far I've only done the basic of tests with no combat tracker running because I don't want to spoil any surprises for my players. So what I know I can do is share two (or more?) maps on the same client screen. And from the DM computer I can move tokens on either map, plus move tokens on maps not displayed on the client screen (either behind the other map or minimized) and that's about it.

Any advice or thoughts?

You can share an image with only some players by dragging the image and dropping it on the character portrait.

I've never tried this with maps but I don't see any reason why it shouldn't work since you can have different player tokens on different maps.

you can do it with maps.

I guess the only problem the OP will have is with the people who are local - i.e. in the same location using the same monitor - when the characters switch between maps both/all will see what's shared even if their character(s) aren't there unless they purposely look away.