Sue
I think your husband's fundamental issue is "why should those who are ignorant of the law be held responsible and punished as if they knew the law?" It seems to me we all have been dancing around this idea. His fundamental beef is "how could the Lord be so unjust and un-merciful?"
I have a few thoughts:
1 - we are all held responsible to the light and knowledge we have, be it little or great. Those who ignorant of the gospel still must repent, given what they knew to be right (even if they didn't accept it). The ignorant are not necessarily innocent!
2- I believe that your husband is applying the "weeping, wailing, and gnashing of teeth" too overly broad. I believe that statement applies to those reject Christ and must take on their own repentance. This is my opinion only.
3 - It's not unreasonable to think that different levels of righteousness can co-exist in the same place. Just like those who do not make and keep temple-level covenants do not enjoy going to the temple, those who have not made the necessary covenants and ordinances will be kept from Spirit Paradise until they do.
4 - Finally, as in all matters, it's a matter of faith. Even if none of our explanations make sense or quiet his concerns, he can either put aside his doubt and pray that the Lord will open his heart to understand His doctrine or your husband won't. I know for myself, I have plenty of questions/issues, but for now, it's enough for me to know that the Savior has my best interest and He will give me what I need to know, when I need to know it. Has your husband asked the Lord to quiet his fears, even if his understanding is not yet complete? In my mind, this is a necessary step, because even if your husband finds an explantion that he accepts, he won't be at peace with the idea until the Spirit confirms the truth of it.
Cheers