It looks as though you wish that “condense” function would already be there… It is one of the major features of Dorico 3, that we are all waiting for 
It’s been stated that it should be available later this year, so a little bit of patience is still needed. You’ll be able to write all solo instrument in their own staff (and have separate parts accordingly), and you’ll be able if needed to condense those instruments on a single staff, and Dorico will adapt dynamically all the necessary markings (a 2, a 3, unison…). A major breakthrough in the notation industry!