M.P.
I suggest you don't have enough information to decide until he has the interview and learns more. They won't expect him to know if he will take the job before an interview, especially when there are 8 people being interviewed. He will get more information. If he decides no to take the job if it's offered they have a second choice.
I suggest you compare the short term difficulties with the long term advantages. I suggest that the children will benefit with Dad's opportunity to grow in his field and earn twice the salary.They will also grow and learn beneficial skills to use their entire lives. Life is constantly changing. Protecting them from that reality isn't always good.
You said with the job.change you.will have money for college. That is important for them. Learning to accept.change and adjust is also important.
Think about why.they were unhappy.for three years snd.see.what.you can change in the next move if there is one. I suggest 3 years.of unhappiness indicates that they need a different approach next time. I also suggest it's.possible that parenting is too child centered with the belief that they should be protected from change. I believe that parents.must consider what is best for the whole family. The adults continued growth is as important as the children's growth. Children lean.about life from their parents.