We have been in that exact position about 2 years ago, my husband was offered a great relocation package to Hongkong or Singapore, after having discussed it with my son we all decided to stay here in the UK.
I think that what made us stay was the fact that the relocation was only for 6 years max and then we all have to go back here, it will just disrupt my sons studies and the hassle of letting our house and all that.
I also was unsure because of the medical aspects of it all, although his pay was higher if one of us ever gets sick, we have to pay for the costs of being in hospital.
Goodluck to you guys, hope u make the right choice for you family. God Bless.