Can one say:
1-What they say is contradictory.
2-What both of them say is contradictory.
3-What they both say is contradictory.
These sentences could mean:
a-They say the same things and the things they say are contradictory. They are condradicting themselves.
but could they also mean:
b-They are saying different things and are contradicting each other.
I don't think the sentences could have meaning "b", but I am not sure.
I think for that meaning one could say:
4-The things they say are contradictory.
5-The things the two of them say are contradictory.
These sentences could still have mean "a" but I think they could have meaning "b" as well.