You will need 20 amps per blower (most blowers surge up to 20 amps at startup and then level off to around 18.5 amps) and they need to be on separate circuits. To determine wattage you multiply voltage by amperage. So the minimum is 4800 watts continuous but you will need the 120v circuits on separate circuit breakers on the generator. We have a 6500 watt generator that cannot run 2 blowers on the 120v outlets because they are on the same 20 amp breaker. To alleviate this problem I made a twist lock adapter to step down the 240v outlet to 120v. This outlet is on a separate breaker. Also need power for fans, clippers, lights, etc....
So the key is enough power on each outlet to operate the equipment needed with out tripping breakers or damaging the generator.