Parallel two solid state relays for improved current handling and avoiding imbalance of load distribution are discussed in this an app note from Vishay. Link here (PDF)
Vishay solid state relay (SSR) outputs can be wired in parallel enabling the user to benefit from lower on-resistance and higher load currents for AC/DC switching applications. This technique is also useful to compensate for load current derating with increased ambient temperature, to minimize heat from output power dissipation, and for circuits that require redundancy. Also, many of Vishay SPST SSRs provide a center tap so that internal MOSFET switches can be paralleled for DC – only switching applications.