it is a very good duty station for families. And yes, English is perfectly sufficient in most situations. Of course, if you live longer in the country, you should make an effort to learn some of the local language but you will not have any problems with English only. Danes are super family friendly and facilities for families are generally really great.
I will move this to the Copenhagen forum – if it is worth moving to CPH for a 11 months or not is of course an individual decision. Would I move my family, worry about schools, sell everything and start a new life? Maybe not. But there are many folks who find CPH very liveable and nice and provided you sorted your accommodation, you should be alright. In fact, I do know at least 3 people who do/did commute to CPH from other countries for a period of time.