Monica and Rick were lovers at some point he was believed dead overseas or something - she ended up marrying his brother, Jeff (as in Steve, Liz and Sarah's father).
Then Rick showed up, eventually she and Jeff divorced. I can't remember exactly how she hooked up with Alan, but when she became pregnant with AJ she had an affair with Rick so didn't know who the father was.
Rick was married to Lesley (Laura's mother) at the time. During a snowstorm, Monica went into labor at the mansion and of course Lesley was there to help deliver the baby and Monica being delirious said that Rick was the father.
I can't remember exactly when Alan tried to kill Rick and Monica - I remember some explosion near the docks or something and then he set up the attic so the roof would fall on Rick and Monica, but then changed his mind tried to save them and ended up having the roof collapse on him
Alan had an affair with Susan Moore and she became pregnant with Jason (Heather's 1st cousin - which makes Jason and Steven 2nd cousins to each other)
