We have a very similar fireplace, it's Art Deco style. My husband glued them together as we struggled to find a match. Not perfect but good enough we felt, so have a go!

The easy solution is to blur this part of the image as is often done to preserve anonymity when there are pictures of family.

Hi, I think that you have to find a line that you can align your larger art pieces on. Not sure how to explain it, so I've made a visual for you. I've put the two smaller pieces together, so they form 'one piece' and aligned the bottom of all large pieces and put the other smaller one between them to form a connection. A common line makes it visually calmer. I've also pulled your chair a little bit forward, to give it some 'breathing space'.

Have a Google for brass sunbursts mirrors, they are typical of Art Deco and come in a huge range of sizes and styles. Beware of so called art deco mirrors cast in brass with a female dancer in the frame, more Art Nouveau and they are mostly poor copies of the originals.