Yep, I had this. Luckily I'd only done a couple more missions after the Uncle one so hadn't got much further in the game. The first time i did the Uncle mission I also the did the bar room brawl mission in Valentine before returning to camp, which is when they disappeared. Saw the thread on Reddit, reloaded an old save and did the Uncle mission again. This time I didn't do the bar room brawl mission, just returned straight to camp and they were all there. I've played on for another 3 or 4 hours now, dome some more missions and they're still all there.