I have a serious vibe about Takeda, feel like he's a spy for the Stepfather, or will set him up for some later event just so he(Fuutarou) would be separated from the Quintuplets.
Man my head hurts sooo much don't know who it is just yet who married the MC. But then again it would get boring if we knew since the beginning. My guess might be the oldest or youngest siblings hopefully miku tho.