Extra style points for the mounting bar geometry and creative coverage option.
+T for helpful photography assistant.
Couple suggestions:
>Might consider partially overlapping the umbrellas. Can probably clip the edge of the underside one to the support arms of the top one. That should provide better central coverage with a less side overhang.
>Might want to shorten the arms to lower the umbrellas to further improve coverage and better deal with wind blown rain.
>Probably need to crank down on that wingnut to prevent the assembly from flopping over to one side in a gust. Lower will present less lever-arm to the wind. A bit of clothes-hanger wire secured to the upper hole in the support bracket extending out to hook around either umbrella arm can serve as support bracket. That's how I support my folding telescopic antenna based mic bar arms in a horizontal orientation.
Trade-offs on having the umbrellas lower are potentially louder droplet impacts, and increased parabolic reflector effect. The parabolic reflector effect amplifies local chatter immediately surrounding the recording position, and can sometimes be heard as an upper-midrange/low-treble peak-filter tone in the ambient background sound floor. A localized version of the under a tent canopy effect. I was walking to lunch yesterday and passed under a new parking awning and this effect was immediately apparent both on the sound of my footsteps and the ambient background noise tonality of water moving in the adjacent waterway.