Toilets clog every two weeks!
Is everything properly vented?  A stopped up vent would be something above the toilets that could cause enough back-pressure to cause a clog.  Check the vent on the roof.

How old is the house?  If you're dealing with something old, you could have a drum trap or some other kludge that could be causing funny effects like repeated clogs.  Furthermore, the house settling could have caused the plumbing to lose the proper pitch.  Improper pitch would mean things wouldn't drain properly, and you'd get clogs.

Do you have a septic system, cesspool, or sewers?  If it's sewers you might have a problem with back pressure from them stopping things up.

It could be a check valve that isn't opening (possibly due to back pressure from the sewers mentioned above).

Do you have young children?  If they put something down the line that they weren't supposed to and it's deep enough that the TVing doesn't catch it, that could be a cause.