If you skip forward a year, so 11, 8, 2.5, 1 then I'd Def have the girls sharing for now. Put down routine for your 2.5 and 1 yo is likely to be quite different so I'd have baby in smallest room, older girls in largest room and middle one in the middle room with any baby overflow of toys and clothes.
In a few years, you can always move them, so SD has smallest room, youngest two (now 4 and 6) have largest room and your eldest gets the middle room