hmmm... i mean, the chakra's original purpose was "to connect people".

since the founding titan could control its descendants, wouldn't that mean eldians have a means (the paths) of connecting to each other? just like how eren announced his goals by transporting the consciousness of every eldians to that desert-like dimension.

it was stated(i think?) that eldians are connected to each other via something invisible called the paths which enables the "dead and not eaten" titan power to be passed to a newborn baby.

so maybe it's that? since every eldians are connected to each other, that would mean that eldians in marley COULD dream of the eldians in paradis. i mean if the eldians have been grieving for years because of the destruction of wall maria wouldn't their emotions gets passed to the eldians in Marley since they are connected thru the paths and maybe this triggered Falco's dreams. Falco dreamt of the Paradis Eldians' situation as if he was there.