My kitchen/family room flow together. I have one paint color in both rooms, but different window treatments, slightly different, but complementary colors because I wanted the rooms to look a little different. Do what pleases you, OP! Even if the French doors are on the same wall, you can certainly have different window treatments! I can see my dining room windows from the kitchen, and the dining room window treatments are completely different from the kitchen/family room. The colors do complement each other, but I want the rooms to look different. That's the fun of decorating!

I have grass shades on my kitchen windows and curtains in the adjoining family room

I have the similar layout and put the same model curtains in different colors (both neutral). Looks good.

Do whatever you think looks good, really!!

I have a kitchen with a window above the sink and french doors to the deck. This all flows (open floor plan) into my family room where I have two windows and french doors to the deck. The two sets of french doors are on the same wall, but clearly in different rooms. You can see all windows/doors from each of the rooms.

My question is...do all the window treatments have to be exactly the same? Or, can I do one fabric in the family room and then a different fabric in the kitchen? As long as they are all neutral and subtle in color, will that work?