I thought the brother-in-law was a sister-in-law. I'm so confused. He had boobies... someone clarify?
Nope, Yashamaru's a guy. Go over in the thread 'Yashamaru: Dude or drag queen' to check it all out.

Secondly, BakaShinji, a headbutt debilitates him AFTER the whole drag down fight. It's Naruto's finishing move, I highly doubt it would have made a difference if Gamabunta hadn't already helped deal with Shukaku, plus, Gaara was woken from his false sleep from it, and we learned from Sasuke vs. Gaara that halting the transformation in the middle has consequences for Gaara.