It looks like they just have a heavier contrast to them, whereas the "Time Fantasy" DLC packs are desaturated a little bit for softer colors. So they'll work, just increase the contrast is all you'll need to do
The most defining feature from these screenshots is definitely the weird perspective, which reminds me of the ever popular Tibia. I don't think I know a whole lot of games that stick to that. Speaking of 90 CRPGs, High Fantasy goes for the pre-rendered look which is what devs went to after this look. But yeah, I don't know of any free or commercial asset pack on that style, unfortunately -- and it'll take alot more than color editing to get this look.
I recommend trying to learn pixel art! This isn't a very hard style to learn, and with the community of artists that we help, hopefully you can get some nice tips!