Hi there, If you get legaly married in Japan then you got adopted her daughter it would be easy to apply for a visa for all of you to come to Spain as a family if the intention is to live and work here, but the laws here in Spain have changed in that any British Citizen NO LONGER needs to have RESIDENCY status to live and work in Spain, all you need to have is a job and to be able to support yourself. If your wife had a visa from the UK Embassy as your spouse she probably could also come to Spain without any problem.

 

You don't need to adopt the child to get a visa for them to move to Spain with you!
If you are married, the child can get a visa as well with no problem, even you are not the legal father.