I'm with you on the first group. I've watched it a score of times and am about 95% certain that's them. Watching it at 25% speed helps.
Video feed cuts in at 11:18:53 (15:36 on YouTube) and in the bottom left corner you see two adults emerge from the trees walking away from the camera. The first one appears to be Alex, as he's wearing a dark jacket and blue jeans, like we see in the photo. The second person appears to be Lori and they are wearing a dark hoodie with a white emblem on the front and white pants. In the photo of her we only see her upper body, but she's wearing a dark hoodie and you can barely make out a white emblem on the front, which is mostly covered by her hair.
At 11:18:56 [Lori] stops, turns around facing the camera, and waits for two [children] to catch up. It is here where you can see the white emblem on the front of her dark hoodie. At 11:18:59 [Alex] stops and turns around also. At this point the two [children] emerge from the trees also. The first one appears to be JJ as he's wearing a darkish [green?] sweater and dark shorts (you can see his calves), as seen in the photo. The second appears to be Tylee as she's wearing a light grey jacket. Where I'm uncertain is it looks like she's also wearing light grey pants, whereas in the photo Tylee is wearing black pants.
At 11:19:00 [Tylee] and [JJ] catch up to [Lori] whereupon she turns back around and begins walking again. Seconds later, at 11:19:04 [Alex] turns back around and begins walking again. This shows that these four are definitely together as a group. At this point two other adults emerge from behind the same trees, just behind the group of four.
From 11:19:13 to 11:19:30 it's hard to make out what is happening. The group of four pass behind the next set of trees, followed quickly by the group of two. As they emerge it appears that the group of two are bypassing the group of four. Yet it no longer appears to be a group of four but rather a group of three...?
Up until the video feed is interrupted at 11:20:06 I can't make sense of what I'm looking at. The group of two hurriedly make their way far ahead of what is supposed to be the group of four. But it seems quite clear that the group of four is now a group of three...
Ok, I've watched it several more times now and I've figured it out! It has become a group of three. The three are [Lori], [Tylee], and [JJ], and they continue on ahead until the feed is interrupted. [Alex], for whatever reason, stops at 11:19:13 behind the tree and appears to bend down. He stays hidden in this position until 11:19:53, a good 40 seconds, when he finally gets back up and continues walking forward at a leisurely pace. What's he doing? Tying his shoes? Looking at something? Collecting some nasty swamp goop for future use?
Whatever he's doing nobody seems to have noticed, except [Lori] who turns around briefly at 11:19:23 to look at him and then continues walking forward with the [children].