A group product is just a wrapper of a group of individual products. I said it is a WRAPPER. What should a wrapper hold is purely depends upon the associated products features. Hence MIN QUANTITY and MAX QUANTITY are not relevant for a grouped product, but which are fully controlled by the configuration of it's individual product.
For an example, Suppose we have a Shoe kit which is a grouped product. Shoe-Kit holds two simple products Adidas-Large and Adidas-Small. In the default case, you should select any one of the above products quantity to 1 in order to add Shoe-Kit to the cart.
Suppose for Adidas-Large You have set min-qty to 3 and for Adidas-Small you have set max-qty to 5. After setup this, if you want to add Shoe-Kit to the cart, you should set the quantity of Adidas-Large at-least 3 and quantity of Adidas-Small should not exceed 5. If any of this rule is violated, you won't be able to add Shoe-Kit to the cart.
Min and Max Quantity of a Grouped Product is completely depends upon it's associated products. If you want to set min and max quantity for a Grouped Product, then you should configure that in it's associated products itself