Pressuring them to get married

I'm pretty annoyed with my parents right now. My son is 17 and got his girlfriend pregnant. She's living with us and they are both working and doing online school. My parents have been telling my kids they need to get married. In my state, since she's pregnant they can legally get married underage. .y parents are stressing them both out trying to push marriage on them. They keep telling them they love each other and already have a daughter on the way so they should just get married. Went as far as finding them a pastor to marry them and agreeing to pay for the marriage license. They don't need to get married, especially if they don't want to. My son's goal is to graduate in December and I think it's fine that he wants to focus on that instead of getting married. My parents also tell me she shouldn't be living here if they aren't married. Well her parents kicked her out and she shares a room with my daughter. I wasn't just gonna throw her to the streets. I wish my parents would butt out. They've both been doing fine. Working their asses off at their jobs and at school. I just want them to graduate. We don't even need to worry about marriage right now.