Both require a suspension of disbelief. Both have female leads filling in for a sister in a way that makes no sense. The Charming Step Mom was a little more fun. She's the One also gives vaguely Well Intended Love vibes too.

Paen Rai Long Tai Wa Rak is modern, but both the female leads pretend to be pregnant to search for clues. Both are comedic and the ML's families are welcoming to the FL.