M.P.
You should really move up there. Your first responsibility is to YOUR kids and not your dad's. You being with your husband and them being with Dad is the most important thing. To be honest I think this is probably the only shot you have for your marriage to stay together if that is what you want. Three years away is a long time-esp when a man has proven himself unfaithful like it seems that yours did. And I will add it does seem that he is choosing this lifestyle and I would wonder why if it were me. It sounds like between his less paying opportunity and his business he wants to start he could possibly make near what he is on the pipeline. Most people would jump at this chance if it meant them being with their family.
I would not run a business for him that's for sure. If he can't take the job opportunity at home and then do the business as well why should you take the responsibility of it. If you do you should make sure that you get a bigger part of the partnership than he does so you are in control of it. And make him sign a contract-DO NOT trust him on this.