Can you add more than one photo/media to an answer? If yes, how do you did it? When I have tried, it replaced the original/?

No you can't

You either have to condense them into one file (using an application like Paint or something a bit more modern) or what you can do is to upload them to a site like imgur.com and then post the links in the question/answer. The only thing with doing it in the second manner is that they don't display online in Y!A, it only shows the links.

You could try uploading to Flickr and posting those links to see if they show online (as Flickr is a Yahoo product). I've never tried it myself.