The picture you show, uses an SSR (a real SSR that controls AC.... The DC S.R.R. in not what we understand as an SSR)
The resistors are connected to the onboard transistors.
They are there to minimize current from controlling I/O-pin. The transistor helps driving enough current to SSRs optocoupler.
The board shown is AC.
Those single DC-parts is probably just transistors+some additional parts rewrapped into a new package