Toddler and baby sharing bedroom

Hi guys! Asking for some thoughts / experiences please. We live in a 4 bed house and have a 2 year old daughter, 12 & 9 year old boy and girl step kids who are with us 4 days a week sometimes more. We are expecting another baby in September. We are undecided whether to turn our tiny downstairs study into a bedroom for the eldest boy, so the toddler, baby and 9 year old can have their own rooms. But unsure whether it’s fair on him, or practical given we will have to find the money to build or buy an outdoor office. Other option is for the 2 year old and baby to share the biggest bedroom. Baby will be in with us for 6 months first though, so by the time they were sharing our DD would be 3, and baby would be 8 months ish. Do we move them in together but keep baby in with us for longer? Or do we not make them share at all and put the eldest downstairs? Please share your thoughts and also experiences if you did have two close in age share (toddler and baby ideally!) Will it work? Thanks! X