well, i mean essentially you 'forced' him to ask you to marry him-to give up and walk out on his wife and kids-that wasn't part of your relationship agreement when you moved to him, was it? I am, frankly, surprised that he agreed. I don't think most people would.
as for understanding his viewpoint...I can't. I was involved for nearly 8 yrs with a married man who swore he loved me, told me i was the only good thing in his unhappy life and that he hoped we would never part ways. That was the last time i heard from him...8 months ago. He and his wife haven't had sex in about 5 years now...she didn't keep up her end of their financial marriage agreement...but whatever she has, he obviously prefers it to what i offer. Your man wants, for whatever reason, to stay with his wife as well.
imho, you are asking your man to re-negotiate your contract after it has been signed, too. you went to him as a poly and now you want him to leave his family and become mono with you. Poly is HARD under the best of circumstances-its nature engenders jealousy and insecurity. It is sharing on the most elemental level-not everyone, including me, can do that.
I don't mean to sound harsh but i think you saw him as your knight in shining armor that would rescue you. well, to an extent, he did...and now you have to pay the price for that. It may be too dear for you. I don't know you and would never presume I know more than what is posted but like Vixtoria said, this isn't a poly attitude you are showing and I doubt youwill find success with this family until you accept the limitations of the situation and learn to work within the framework of this family.
And, no, you probably never will be welcomed by their families...most people don't understand or approve of a poly lifestyle.