O.P., you should read JackMDS' links carefully. With your double-router setup, it'd be impossible for PC1 to "see" PC2 or PC3.
SOHO routers are "one-way". PC connected to the "internal" ports can see each other and can see out, but PCs connected to the "external" port cannot see in. If you want all the PCs to "see" each other, do not connect ANYTHING to the "external" port of the secondary router. Put a piece of tape over the port to avoid accidentally using it.