is this eating apples you are cooking with or bramleys? with bramleys i cook gently in saucepan for a short while. but havent used eating apples for crumble. i believe they are probably much softer <<havent a clue>>
Bramleys cook very quickly so it is unlikely that they will be hard if you don't cook them before putting the crumble topping on. However, I often part cook them in the microwave in the baking dish (cuts down on washing up) before putting topping on and placing in the oven.
I'm making apple and blackberry crumble today. I just slice eating apples and use them with whole blackberries, but of sugar, small splash of water and top with the crumble (slightly more flour to butter and some brown sugar) I never measure, just do it by sight but there's a recipe here