They are very cheap.

You are very generous.

Their $4 barely covered the potato chips they ate.

(And the part about them splitting the bill while you can't drink and they ordered bottles of wine.....rude, rude, rude. Next time, point out to them that you aren't drinking.)

This is how the 'rich' get richer. Trust me, they aren't rich in what matters.

Best of luck with the baby!