To the original post. My advice is this. Judging by your ages alone you are both grown adults. ASSUMING that you both DO know each other well, why on earth are you stressing about something so simple?
With the attitude you have at the moment, I'D BE SCARED!!! Because you're making it SEEM like a big deal. Just because someone meets your parents, it doesn't mean that you are introducing them because marriage is in the air. It's not 1956 anymore so stop panicking woman!!!
Honestly, it's simple. You are seeing each other and your family are an extension of you. End of.
Just offer casually that you have something going on at the weekend, you'd like him to join in and be there but if he has plans that's fine. End of. What's the big deal? LOL