The answer will depend on whether the hexagons are all the same size or not, whether they come together in a plane or 3-dimensions, whether they can join at vertices or only sides.
Two hexagons, of the same size, that are coplanar can make a concave hendecagon (meet at side) or a concave dodecagon (meet at vertex).
Two concave hexagons can also join (dovetail) to make one hexagon.
The question is under-specified.
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