I need advice!

Okay Glow Friends, I'm in need of your advice. I am the oldest of two sisters who are twins. I am currently married (4yrs) with 2 kids, one of my younger sister is married (4yrs) with 1kid. My other sister is in a relationship with a guy who is married (needed for green card). We just found out she is currently TTC, we have constantly told her to use protection until the guy figures out what the hell he is going to do with his life. She still lives with my parents, & he lives with his mom. He is not living with the wife, but wife still pays for his bills. We have told her how expensive children are and how she is going to pay for everything when she works in retail making minimum wage. The guy also works minimum wage. She told us to leave her alone and let her live her own life. She complained to my parents about us gaining on her. What do you think I should do? I hate to see my sister suffer & be tied down to a man who just needs her as a backup plan.