I am looking for a double sleeping bag, which will be used for car camping and my travel destinations will not exceed 35 degree. I am able to figure out below bags. First one seems to be cheapest, good brand and can open up as a blanket, but I need some experts advise so that I should not end up paying at wrong bag.North face Dolomite 3s double 20 Degree (119 $)Mountainsmith Loveland 30 Degree (180 $)Big Agnes Cabin Creek 15 Degree Sleeping Bag (189 $)
Virtually all sleeping bags can be mated with the same model, even different models within a brand and style range. In fact the best arrangement for two people using a sleeping bag for car campig is to buy two rectangular bags of compatible models and zipper arrangements, one a 35 degree rated summer weight bag and the other a 10 or 15 degree 3 season rated bag. Since your body weight compresses the bag underneath, the lower bag provides minimal insulation. In mild weather you sleep with the 35 degree bag on top. For cooler nights you flip the heavier bag over you and sleep with the summer weight bag under neath you. There is no need to pay a premium for a double bag.
Buy two single bags from the same manufacturer. You can open and zip together to make a double. Much cheaper then a double. Also can be used as a single when needed.
Buy a left-handed zipper and a right-handed zipper sleeping bag. Then, zip them together. You should spend $500 on two properly-rated +15 down sleeping bags.
