  Using extended coherent states, an analytical exact study has been carried
out for the quantum Rabi model (QRM) with two arbitrary qubits in a very
concise way. The $G$-functions with $2 \times 2$ determinants are generally
derived. For the same coupling constants, the simplest $G$-function, resembling
that in the one-qubit QRM, can be obtained. Zeros of the $G$-function yield the
whole regular spectrum. The exceptional eigenvalues, which do not belong to the
zeros of the $G$ function, are obtained in the closed form. The Dark states in
the case of the same coupling can be detected clearly in a continued-fraction
technique. The present concise solution is conceptually clear and practically
feasible to the general two-qubit QRM and therefore has many applications.
