Thanks ladies, I feel reassured

Our intention has always been to move them into the same room once DD2 starts sleeping through. But she might actually start doing that if she's in bed with DD1 rather than me or DP co-sleeping with her once she wakes up (normally around 1am).

We have a double bed in DD2's room too so I'll go and sleep in that. Lucky we bought that 4-bedroomed house then - three of us sleeping in one room