I love the artwork, b/w is chic and soothing. I also love the batik pillows, put those in front! Look for something else with those green or blue hues, maybe a pair of new bedside lamps with ceramic bases in those watery colors, slightly bigger lamps would look great.

I would look at burgundy

would like to know the dimensions of the sunbrella cushions for 6-Piece Giva Outdoor Teak Sofa Set With Sunbrella Cushions. https://www.houzz.com/products/6-piece-giva-outdoor-teak-sofa-set-with-sunbrella-cushions-spectrum-eggshell-prvw-vr~124317642

There are some good foam spray adhesives out there. I used some to glue 2 cut scraps into one chair seat. But sometimes couch cushions are rounded on the edges, which wouldn't work good for an overall smooth look imo. Do the covers come off for you to inspect the foam inside? That would be the first step to check out. If they are equal sizes with smooth cuts and 90 corners, then I'd probably try gluing them together first and see how it looks and works. Worst case, it sucks and you buy new foam, which you may do anyway. I have a local foam store where I purchase my supplies, so maybe google that in your area. They have all kinds of foam options (thickness, firmness, etc) with higher quality at competitive prices to hobby stores. As far as reusing the fabric, I don't think that would look good to have a seam down the middle, plus you wouldn't have any allowances left. So buy new of that. I have found many great tutorials and products on this website, including this adhesive. adhesive: https://www.sailrite.com/NG633-Foam-Lock-Spray-Adhesive-12oz