This work is concerned with the passive realizability problem for a biquadratic impedance with double poles and zeros as a seven-element series-parallel RLC (damper-spring-inerter) network, which is a series or a parallel connection of two networks: a three-element series-parallel network and a four-element series-parallel network. First, a necessary and sufficient condition is obtained for the realizability of a biquadratic impedance with double poles and zeros as a series-parallel network containing no more than six elements (see Theorem 1). Then, the main theorem is presented (see Theorem 2), which is derived for three-reactiveelement, four-reactive-element, and five-reactive-element settings, respectively (see Lemmas 2-4). The results can be directly utilized to physically construct a passive mechanism containing dampers, springs, and inerters, which can be regarded as a passive controller for some mechanical control systems.