You can solve it by this way also.

Which door would you point to if I asked you the question which door is
the Life door?

Both should point to the Life door!

If you think of T (true) and F (false) as functions on the parameter Q
(question), the T person would reply T(T(Q))=T(Q) and the F person would
reply: F(F(Q))=T(Q).

For the previous soln, one replies T(F(Q))=F(Q) and the other