Welcome to the Core 🙂
You've posted this in the 'Joints' section, yet there don't appear to be any of those in your scene, and the question is about Object Manager hierarchy if I understand it correctly, which I am not entirely sure I do...
It is not possible to make 2 parents of a single child, but that shouldn't be what you are aiming to do here, so shouldn't be an issue.
You haven't said how you plan to 'connect' each end of the spline driving the sweeps to the parts at each end, or how you were planning to animate them, but you wouldn't do it with hierarchy and parenting.
My advice would be use spline dynamics on the splines driving the sweeps, and create 2 null objects as children of the battery and the ear. Then you could use clamp constraint tags to fix each end point of the spline to its respective null meaning that hopefully the spline goes wherever the things they are connected to do...
CBR