Complex sentence: Soun let his daughters decide amongst themselves whichever should take up the engagement, but after Ranma's gender-bending nature was exposed, the two older sisters foisted him/her on Akane.
Split into simpler sentences: Soun let his daughters decide amongst themselves whichever should take up the engagement. But after Ranma's gender-bending nature was exposed, the two older sisters foisted him/her on Akane.