My son is 10, and growing like a weed, BUT for now we can hang both of our hammocks under one tarp.
I simply hang his hammock above mine.
I am sure there would be some added difficulty with grown folks, but for now its working for us.
Ive got the Neo gear guide 9x9 square tarp, and I can get it pretty low and tight over us with this setup, been dry in all but the windiest of rains so far in our backyard testings.