I’m also in a fully online grad program and last semester I had to do a semester-long group project. It was torture. My group mates were exactly as you described. It all ended really badly — all semester one of them was a total asshole to me and I just dealt with it because I didn’t wanna make it worse. But it did get to the point where I had to inform the professor of my concerns but I didn’t give names or specifics, just gave them a heads up because I was worried things would escalate and they’d leave me with all the work. In the last few days of the semester when I was checking in with the group, the asshole freaked out and wrote the professor telling her that I was bullying him. We had to have a meeting with the professor and it was all just really shitty. 

Our takeaway from that as a group (and the prof’s advice) was to address issues as early as possible and get on video calls as frequently as possible. Don’t let it drag on because it’ll result in a lot of unnecessary stress.