"Coming Home"

(Cover credits to http://bollatay.deviantart.com/art/moar-spn-stuff-333482043) 

Dean has been in a long going relationship for 10 years now with his boyfriend Castiel. His brother, Sam, has been in an equally long relationship for about a week less, with Castiel's brother Gabriel. Marrying your in-law seems kind of strange, so Dean and Gabriel are trying to get Sam and Castiel to propose first. Which couple will be wed first and which will awkwardly marry their in-law?