Ask your aunties if they are making cakes with margarine or butter. All the margarines on the market now don't take too kindly to being creamed for too long - their substances break down and begin to curdle. If they are proper old baking aunties, they'll be trying to beat the sugar in with the marg until the crystals break down before adding the eggs. It cannae take it, Captain!
I usually make my cakes with butter, however, a few weeks ago, I had to make an emergency cake for someone and didn't have time to let the butter come to room temp first, so I went off and purchased a pot of Stork (the old fashioned cake-maker's fat of choice). Started the old creaming process with the sugar, whole thing went like a science project long before the sugar had dissolved. When I phoned the Stork care line, a 12 year old told me I'd beaten it too long. When I questioned this child expert, I was told that their Home Economists make cakes from it all the time and see no need to cream anything too thoroughly. Wonder where they learnt to cook? Hope that's useful (if longwinded!) Tell the aunts to go back to butter.