Freezer as a fermentation chamber

Hoping someone could tell me what size chest freezer I would need to hold two 6.5 gallon carboys plus a blow off bucket n the hump.

I don't know that carboys come in standard dimensions, so you'll have to do some measurements and research. I did see a thread or two on here that had illustrations of how many 5 gallon corny keys would fit into certain brands of chest freezer - but corny kegs are standard diameter/height. I think your best bet is to go online and lookup internal dimensions of some chest freezers that you can easily get your hands on and see which ones will fit carboys of your diameter and height.

At least 7 cu ft. My 5 will only hold 1 6.5 gal and 2 3 gal carboys.