i think it all depends on what you want to do with them ...
what size room is it ? do you want the whole room lit up like a xmas tree or
a light here, and a light there, to accent the light already there / available ?

... with umbrellas you will get some light but you still will not light up a whole room
an idea might be to extend your light stands and lights all the way up, use umbrellas
and then without them and see how the light looks ... ( how many do you have ? )

you might to get a basic book on architectural and portrait lighting .. it will give you better ideas
than i can suggest from 3000 miles away and an internet connection

john