Parent Shipping Classes

Hi

If I have some sub-classes under a parent shipping class, is there any way to set conditions on the whole group?

Our example: the parent class is called “P&P” which contains 7 different products. In the store, I want to limit it so that nobody can buy more than 19 TOTAL boxes, but they might have a mixture of say 15 of product 1, 2 of product 2 and 3 of product 3. This would total 20 items, so I would like it to then say that shipping isn’t available (the customer would then contact us).

I have tried putting “P&P” in the table with max items 19, but it seems to make no difference to individual items. I was just wondering if this was possible in any way?

Thanks

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