You can’t. Pressuring people backfires. There are so many issues involved in these decisions, and it’s unlikely you know all the issues involved, and at the end of the day, people have to decide for themselves when they are ready to get married. It’s a really bad idea (most of the time) to pressure someone to date when she doesn’t want to.
btw, I just reread your question – the way it is phrased, it sounds like your friends are waiting until they have 2-5 kids before they get married! If that is the case, then yeah, you should speak to them about it. Or change your friends.