Eventually, at a certain age, especially for your eldest daughter....they will "need" their own room.... they develop differently and she will need more privacy and just her own space.
for now, they are still young... so it might be fine to combine them... but a child that age(s) should be talked to about it first... and asked their feelings on it... and that they know it does not have to be, "permanent." They are used to having their own room.... and might want it to stay the same. That should be respected. To me.
A playroom, is not the same as having their own room.
I shared a room with my sister growing up, we are 2 years apart. But after a certain age, it was just unbearable... we were so different from each other, we had our own preferences to things and ideas and tastes and needs for privacy and different habits... so at about the 2nd grade or so, we had our own rooms.
Some siblings don't mind being together... some do mind. Mostly, for friends I know, their children started off from the get go, being in the same room... THEN, when they were older, they each got their own room.... and this is a natural progression for children... since they develop more, change and have different needs as they grow up. AND.. .the older children get, the more pronounced the differences in age gets... developmentally. There is a big difference for example, between a 3 year old and a 5 year old. Even if it is just 2 years. For my friend, she separated her kids when her daughter was 6-7 years old... and her sibling was 2 years younger as well.
Regardless, it needs to be discussed with the children first... and have a trial period, maybe. Personally, as a child, at that age, I did not like thinking that my sense of privacy was uncontrolled or that I had no input in the matter. My sister and I fought a lot when sharing a room... and my older sister would just boss me around and push my things away and she took up most of the room. It was just frustrating. And we had a big playroom too... didn't matter... a playroom is not the same as a bedroom. A bedroom is a special place for a child.
Personally... I would leave them the way they are...
All the best,