I have just moved into my new place for about a week. We have decided to stay for 4 days at our own place and 3 days back at in laws place so that its nearer for the kids to commute to the school and also still able to spend time with the grandparents. However after trying out for one week, it seems like the kids are having difficulty sleeping for the first night at each place. Is this a bad idea for 21 months old? Should I just stay at one place?

i would choose to disagree and say that you need to stay in one place to give the kids some stability. it may be fine for you and your partner to adjust, but for the kids, staying for a few days here, then there, can cause too much chaos, and disrupt their regular life and routine. stick to one place. let them adjust and feel comfortable. you can always take them over to the grandparents and spend the day. or the grandparents can come and stay. also, instead of going and staying every weekend, make the night stay a once a month affair