Tomato problems

'Double' flowers tend to be sterile. Could you put up a photo of the flowers please. You can just add it by editing your question

If they are just large,open blooms with multiple petals, many of the Beefsteak varieties do this, but their pollen is also among the most sensitive to extreme temperatures. If they are in a greenhouse that gets quite hot in the day, try ventilating it better. If they are in the open, but the nights have been sweater-worthy, try putting them under cloches, to hold in the heat at night.