If you want to get vision aids and eye protection from sunglasses, you can just order a pair of prescription sunglasses which made of prescription lenses that fit for your eyes. If you just want to insert prescription lenses into your plastic sunglasses, it may not achieved unless it is a fitover sunglasses. Or you can try clip on sunglasses that also available for people need vision aids.
That may depend. It may depend on the size of your lenses and your sunglasses frame. If your lenses are smaller than your sunglasses frame, this way will not work. If your lenses are bigger or just the same as your frame, some specialists may help you make you dream come true. In fact, there are a lot of cheap and fantastic frames online. You can get a new pair of glasses without any trouble. It is no need to be such troublesome. There are even some free glasses available online such as Firmoo and coast.com. You may have a look.