The add to cart and wishlist buttons should be fairly easy to accomplish, but you will have difficulties with the quantity for the buy now button since the buy now button will need to be in a separate form.
the code would look like:
onChange="document.<formName>.<hiddenQuantityField>.value = document.<formName>.<QuantityField>.value">
replace <formName> with the name of the form, remember, you will have 2 of them, so you will need to get the right one for the regular quantity field and the hidden quantity field. also replace <hiddenQuantityField> and <QuantityField> with the correct names for the form elements.