Room sharing with toddler and baby

So i just found put I'm pregnant and moving into a 2br apartment. Our original plan was to give my 8yo stepson the 2nd bedroom & have me the hubby and our 2 yo girl sleep in the master ... Now I'm not sure how to do the sleeping arrangements since there will be a new addition .. We were not able to find an affordable 3br so that is out of the question ... Does anyone have any advice?