Urggh those crescents. Well after a long time loading 120 on the patterson reels in a changing bag, with the odd film getting jammed, I read somewhere the best way was to unroll the film when you are ready to load it (in a dark room ofcourse!) let it hang (having untaped it from the plastic film sprocket thing) and load it onto the reel as normal. Never had a problem since. Something to do with the weight of the 120 film? Anyway, don't have the problem with 35mm, which loads just fine in the changing bag. Oh and by the way, sweaty hands...not good for loading film...seems to affect the friction or something.
By the way, it does not matter whether your tank holds two 120 reels or 1 reel, since the reel is probably pretty much standard diameter and width (width set by the 120 film itself!), the amount you will need per reel does not change much. If they are all similar between brands, then the amount you will need is about 500ml of chemistry for one reel of 120 film. K