The Morning Calm member has four lounge passes - all they do is scan their boarding pass at the lounge to enter. No physical passes or coupons. And, the member can let in non-morning calm members. The Korean language website just says "accompanying passengers flying Korean Air flights can enter" but it doesn't specify "maximum one person." Like nowhere on the page it says that haha so it SHOULD be fine for you two let two in with your passes.

Otherwise, just pay 4,000 miles. It's not the best value, but it's not THAT bad. It's around 50-60 USD which is what most airline (not private brand) lounges charge anyway