John is absolutely right about loads... If you do go with the WV/Boberdized $2000 system you do have to figure what it takes to run stuff and some stuff you won't be able to run, even with a 7500 Watt generator... But given that yer parents allready heat with oil and don't have to run a submersible pump or heat water with electricity then the 7500 W unit will do pretty well for the rest of their needs... An electric oven or clothes dryer are big drains so I would try to use smaller appliances such as the microwave or toaster oven while on generator...
Another couple factors... The WV/Boberdized system with a $1200 7500 Watt generator isn't going to be electric start so yer dad is going to have to pull the cord like starting a lawn mower... Also, most hold about 5-6 gallons of fuel which, depending on the current draw, will only last 12 or so hours...