Please describe your options conditions a bit further.
If your options are to size or color or something like that, and your customer is only buying one of the options, say they want 3 of the red ones, then the quantity is managed in the normal method by input in the qty field on the product page.
However, if you are wanting to allow them to buy 2 red and 3 blue on the same product page at the same there is currently no way to do that in the options. They need to buy the red ones and then buy the blue ones.
If the second condition is your goal, but might look at our extension where we treat Products as options.
https://marketplace.abantecart.com/product_as_optionIt was designed to add the stock tracking of products that are add-ons to a product.