Gah! I can't save / free the Winters Family! At least right now. I obtained the quest from Frank Weathers while at Aerotech by pure chance. BUT, I had a 'Vilified' status with the legion pre 'Ring-A-Ding Ding!'. I'm thinking, "Damn, I want to save this family!"
Fast forward to post 'Ring-A-Ding Ding', and Volpes Inculta accosts me with that creepy arsed vibe of his, and as you know, gives me The Mark of Caesar. I'm thinking "Great! I can do this now!" I make my way to Cottonwood Cove, but forgot I was also granted the 'Render Unto Caesar' quest. Uh-oh. I kept trying to get Canyon Runner to let me purchase the family, but he keeps going on about getting to the dock, get on the boat, blah, blah.

Maybe I can make a pre-quest save, get on the boat, and see what happens from there? I'm leery of the whole situation though. Because if I understand it correctly, completing 'Render Unto Caesar' will place the game in a direction I don't want.

You could just shoot up Cottonwood Cove and take the key out of Canyon Runners cold dead hands. That makes everyone at the Fort hostile, but you can just kill everyone there. That makes you fail Render unto Caesar.

You do not have to follow the whole questline through and ally with the Legion. Pragmatically speaking, it's best to just visit Caesar and get it out of the way, possibly netting yourself some Legion fame and decent amount of XP along the way. You have to travel there either way if you are going the Mr. House route or Yes Man. You can either stay on the Legion's good side for the time being or slaughter them starting at Cottonwood Cove, or alternately sneak kill the entire Legion presence at Cottonwood except for the raft guy and then release the family. The raft guy will become hostile once you release the fams, but it's possible to sneak out of there without engaging him or taking a hit to your reputation. Killing him will result in the quest failure for Render Unto Caesar and gain Legion infamy regardless of how he dies.

Buy there freedom from canyon runner after your trip to the fort.

You can actually finish the quest with Caesar being happy if you go against what he wants.

Afterwards go free them and then go which ever path you want.