I had a fairly easy time acquiring the online trophies. It's possible I just had good luck and/or good timing in finding the right companions.
I took this advice for the Companion trophy and got it on my second attempt. For my first attempt, another player with a very long scarf spawned right away, but they seemed more interested in attempting to fly over the beginning gate (the one you emerge out of) to see what was up there. I left that person to their own endeavors and found another companion about halfway through the snow level, finished the game with that person, but apparently it wasn't enough time together to count for Companion. On my second attempt another player spawned right away and stayed with me until the end.
A couple pieces of anecdotal advice from my experience:
1. In addition to sticking close to your companion, try to find another way to make it clear you want to stay together until the end. During the first vertical section, where you fly up the pieces of cloth to various platforms, I went first and waited on each platform until my companion caught up with me to try and make it as clear as possible that I wanted to stay together.
2. You will almost certainly become separated from your companion during the final flight section, especially if their gameplay experience is less than yours. My advice here is to proceed to the end as quickly as possible and then wait for your companion. If your companion is equally as adept with the flying mechanics, you should arrive around the same time and all is good. If they are not as accustomed to the flight mechanics and get hung up, or if they do some sightseeing along the way, you want to make sure you don't dawdle and arrive after them, lest they think you abandoned them and ended the game without them. This may require a bit of patience; in my successful second attempt, I arrived at the summit about 3 minutes before my companion. Around the two minute mark I was beginning to wonder if they had quit or finished without me, but the wait paid off when they finally arrived.
For the Reflection trophy, I think I just had good luck and came across someone who had paused or suspended their game, as they were already sitting when I spotted them. I sat down for 20 seconds and poof, trophy.