If you assign a group to the pool (assuming flexible pool type) the system will assign a random desktop to any member of this group who tries to log in. Once they log out, the recycle policy is adhered to which will ultimately make the same desktop available to another user later.
If you mean you wish to assign desktopA to both users1 and users2 then no, you cannot do this as the system would not know how to handle two users trying to log in at once ... think of in a physical PC environment you couldn't achieve this without a fight on who sat down first.
A bit more info from you on what you're trying to achieve will help us help you find a solution.
Hope this helps.