Tag implication: twincest -> twins
Reason:
twincest is incest between twins. There doesn't really seem to be a problem with them being tagged incest as well, but several pages of posts tagged twincest are not tagged twins. Since there are twins in these images, they should still show up in a search for twins even though they are also tagged twincest.
An alternative solution would be to do away with the twincest tag, and make sure that all of the images currently in it are properly tagged twins. It doesn't appear to be used that much, with under 200 images tagged. incest twins should theoretically return pretty much the same results. Of course, this could limit the ability of normal users to find the images currently tagged twincest, since it would require both of their two tags to search for it.
EDIT: After thinking about it, that problem exists with searching for other specific forms of incest as well.
Updated by a moderator