There doesn't seem to be anything 'concrete' that I can find. I can only think they'd be the same age as my grandparents (Neville and June), 3 of mine are all cremated because 'they didn't want someone having to be put out tending the grave stone'. It might be nothing sinister 9but it might), plus I'd imagine how many burial plots were awailable in the area and if there was space to buy them together if they wanted that.
I have read on another site that it would be June's religious belief to be buried but I'm not aware as to what religion she followed or whether she went to church that didn't specify instruction for death, most religions now accept that due to burial plots being 'sparce' that cremation is allowed where necessary and I'd assume if someone hadn't specified, that a cremation would have taken place.
From what I've been reading, its usually parent who have lost children that prefer to have a burial, I can understand that.