If the back ones are more than 50% worn I would replace all four. If they are less than that, I'd probably put two new ones on the front and start rotating them about every 10,000 miles so they wear more evenly.
Around here, the stores that specialize in tires (Hibdons, Robertson Tires, Discount Tires, etc) will rotate them free of charge, especially if you bought them there and sometimes even if you didn't.
Douglas is apparently made by Goodyear specifically for Walmart Stores. I've used them, they are decent tires for the money. They're usually a budget tire.
A guy at a regular tire store told me that the same tire (I was specifically looking at Michelin Defender) that the tire stores carry is not the same tire that Walmart, Costco, etc. carries. He said Michelin makes a cheaper tire for the discount stores and one from any tire store would be better quality. No idea if that's true, but that was his claim.
Some tire stores will price match, so I would look at some websites (including Walmart, Costco, etc) and then google some tire stores and see if anyone in your area does that. Robertson Tires gave me the same price for the Michelins as Costco, and the service was terrific.
Aries
~Sign of the Rams
