LOL. Our kids are the same age.
We finally figured out that the Womb Raider was throwing Mr W under the bus. My MIL was taking her side no matter what yet it was usually when she wanted something her brother had...
The new rule is that if neither of us saw it, its her fault. After a week of this, she has nearly stopped the boo-hoo-woe-is-me act.
Mr W cannot lie and the WR is virtually indestructible physically. (At 18 mos she likes to jump off the diving board...)
They will play together for hours with Mr W occasionally coming to us to tell us she has climbed up the drapes or something like it...