The 6 mutfruit trees and 12 other crops is correct. You can find out who is attending what by going into build mode, and highlight the person. Anything they're assigned to will also turn green. Of course, getting the line of sight is tricky.
What I did was put the bell in the center of my crops. I ring it, then they circle around the bell. I highlight them, and then wrap the camera around to see the crops. Works out nice.
Be mindful you do not need to assign every plant. Thankfully, Bethesda saw this was going to be irritating and helped us out by having the settler take the unassigned crops around the one you select. The settler will take 12 0.5 or 6 1 fruit if they're next to each other.
Starting out, of course, you may have settlers doing different crops. You can re-assign them if a specific crop has grown in size. For example, I had one settler doing razorgrain and tatos, but once I got more settlers, I just re-assigned him to razorgrain completely. He does all 12 plants now.
Even if the "person" icon is green, you can still re-assign. This helps manage settlers. It takes patience and time.
Tip: Take all the Raider Left Leg armor you can get. Pretty much on most of them. Then, give them to settlers who are assigned. Fast way to tell them apart. I use raider gear because it's the most abundant out there.
Hope this helps.