It's a matter of opinion (and finances) whether dry is better than wet food and vice versa. The Dog Food Advisor has something to say on this subject - link.
They are less processed than dry food and the better quality ones have a high meat content. They are palatable so good for picky eaters.
I looked back on your previous post and I assume that you would like to feed both dogs the same food. Due to their health and history I feel that wet food would be a good choice. The underweight one would have more calories and the fussy one would enjoy the food more than dry.
Of the wet foods that you mention, Forthglade might be the most economical but TBH I haven't priced them up. I've used it on occasions when Morrisons have had it on offer for £1 per tray. Usually they have the grain free in stock but I quite like the recipe of the brown rice versions. I usually just replace one meal with it for a change from their usual cold pressed and it seems to work OK. Tesco also sometimes have Forthglade on offer too. Anyway, I looked on Berriewoods website and buying in bulk brings the price down to something like 96p per tray.
The good thing about Forthglade is the range of flavours so hopefully that would suit your fussy dog. Natures Menu do a nice range of flavours too but for Greyhounds I think you might need to look at the 600g tins and maybe mix them with something. Their Mighty Mixer would be good but I am not sure whether your dog with dental problems would manage it because the cubes are very hard and crunchy.
Cold pressed food could be a good choice and should suit both dogs. The pieces are not too hard to chew and you can soften it with water to make a wet food to your chosen consistency.
As for mixing foods, using wet food as a topper on dry food seems to be popular these days. As long as the dog has a good digestive system and it causes no issues than there shouldn't be a problem. However, if a dog has intolerance or has a sensitive digestion then maybe it is best just to stick with one product. Also, the owner needs to remember to cut down the dry food so that the dog doesn't become overweight.