No, sorry to report that he said nothing about Della's husband, and there is no info on Hortense and Quackmore either.
But I think you're right, that firecracker probably didn't kill Della's husband. Maybe its simply was the last straw for him, and he left the family... and then Della tried being a single mother, got fed up with it and ran off as well.
I dunno, that's just me theorizing. It does paint HD&L's parents in a bad light, but in some ways it makes sense that they were originally raised by bad parents, judging by what absolute terrors they were in their earlier days. According to Barks, their parents raised them with extreme permissiveness, so they thought they could get away with everything. Even if Donald is hardly a model parent, it seems he does a better job than their real parents did -- the kids are hardly angels even now, but they are much more well-behaved and considerate. (Joining the Junior Woodchucks probably helped straighten them out as well.)
As for Scrooge not contacting Matilda, it's because he doesn't know where she is. She cut all contact with him and made it absolutely clear that she wanted nothing to do with him, even moving away without leaving a return address. Scrooge didn't even know that the new caretaker of McDuck Castle was his own sister -- only Donald knew, and Matilda made him promise not to tell.
Man, it's easy to get me talking up a storm about the Disney Ducks... side effect of being a Donaldist, I suppose.