Don’t read this if you haven’t finished the Mortal Instruments!
Jace and Clary end the Mortal Instruments at sixteen and seventeen years old. Bit young to get married in this day and age. They appear as characters in The Dark Artifices, which takes place five years later, and in the series that comes after that (The Wicked Powers) so it’s entirely possible you’ll see a wedding for them in a future book.
The same answer goes for Magnus and Alec, Isabelle and Simon, Maia and Bat — as well as questions about whether they have children. The characters from TMI continue to be mentioned in The Dark Artifices and after. You’ll have to keep reading to find out!