This fall into the category ... what you always wanted to know about Dark Shadows but were afraid to ask. Or love among the shadows.
The only two couples I can think of off-hand who definitely had made love during the run of DS were Carolyn/Jeb and Bramwell/Catherine. 1795 Barn and Angie had almost without a doubt, been lovers in pre-DS days, so I'm not counting them.
Am I forgetting someone?
Incidentally, this is one aspect I miss about classic film and television; the romantic subtlety they used in love scenes, leaving so much more to our fertile imaginations. There were many scenes in DS which sizzled with romantic and erotic tension. Quentin/Beth and Catherine/Bramwell, to name only two, but there are many more!
Happybat, ever the romantic