I have a 30 AMP breaker and circuit feeding 10 gauge wire to several 15 AMP outlets. However, some of these outlets also have 12 and 14 gauge wire feeding off them to other outlets, light fixtures and switches. Doesn't this present a possible fire/short circuit hazard if one of the 12/14 gauge wires becomes overloaded?

Sure does present a fire hazard.

With the #14 wire in the circuit, the breaker needs to be a 15 amp.

Also, understand that you CANNOT feed standard 15 or 20A receptacles from a 30A circuit, even if it is wired with all #10.