Not sure you can get to your C on the map. Others have been stopped going through the Mayan property to get to that side of the estuary'. See below how to get to the other side of the La Pinta estuary at the Mayan Golf.
You can add the tip of the peninsula that is Las conchas. This is the other side of the estero Marua, from number 3 on your map. Take the turn off to Las conchas from Fremont just past the Pemex and Oxxo at Josefa/ Drive all the way through Las conchas development ( about 6 miles) on the main dirt road till you get to the end at the big high rise, Tessoro. If you have a good 4WD you can drive over the big dune right to the shore. Alternatively park at the end of the road and walk down to the beach over the big dune. This is much easier to get to than all the way around to the other side of the Marua estuary and your number 3.
Also you can add the other side from your C on the Mayan at Estero La Pinta. No fussing with the Mayan folks. Just continue on Fremont, which turns into the highway to Caborca and the Mayan. Go past the entrance to the Mayan a couple of miles on the highway and watch for an old abandoned adobe structure on the right hand side of the road. At that juncture there is a very wide road off to the right (and one to the left as well) that leads to the estero La Pinta. (Someone else, Stuart or Kenny, here can provide the Km Market number) . The turn off road can been viewed on Google Maps and it is the largest you will come to. You will say "Wow that's a wide road"!!. The road is in decent condition no 4WD needed. It is about 3/4 miles to the estero. You will end up on the other side from the Mayan Campo de Golf. An abandoned hacienda and lots of pangas here. safe and secure just don't take a dog !
Both of these alternatives will lead you to fish on the same estuaries just the other shore from your map. They are much easier to get to as well. Have fun and good luck. Maybe I'll see you there.