LOOL this is so good! I honestly thought the middle was a little slow (it was more like a slice of life with daily events) but the beginning was strong, and it definitely picked back up in the last few chapters! I think his plan might be that if they get together and plan to get married, then the in-laws are less inclined to fall for each other since they're relatives. (although it would be perfectly legal/fine and normal for them to still marry each other even after the ML/FL get married, they might be less likely to since they perceive each other as their sibling's significant other's sibling and related)