Hi pam,
May I first start off with I'm terribly sorry for your loss and I can only imagine how rough it was/is and the changes you had to go through raising four boys on your own. ::big hugs:
Now, about your dream - this is my take on it: A recurring dream about your husband returning, but he would return with amnesia and you would find out he had another family; I would imagine you had these dreams early on... closer to when he passed. This was your minds way of telling you you've passed the grieving stage and it's time to pick up the pieces and move forward. Not in the sense that you should forget him, I think that was why you had the dream it was telling you life will go on, it doesn't mean you will forget him. One never forgets, but time heals and as time goes by, it gets a little easier with each passing day.
The latter part of your recurring dreams where he returns and you don't know how he will fit in means you have apparently succeeded, I'm sure with some road blocks and challenges of course, in raising four boys, running a household and making ends meet. Most importantly through this you have gained independence, confidence and you know there is nothing you aren't capable of. I think this is like a mental pat on the back, a kudos from you to you

And you deserve it!!! A job well done! It isn't a dream of compatibility.. these are good dreams.. healthy dreams and by those dreams I can see you have a very healthy attitude with your misfortune and I'm certain your boys do too. It means you have coped well with all things considered.
I hope this was helpful.
Angelique