As a PA with an uncooperative member of the team, I would try to get some one on one time with them to figure out the situation. As others have mentioned there could be an underlining reason why they are unresponsive, whether that be personal reasons or work related. Once the situation is assessed and the details are out, I could work with them on trying to work around their situation so that they still could be of use to the team. If the reason is that just they are lazy and don’t want to put in the effort, then that’s a whole different story. Depending on the severity of their impact on the project, I could ask for them to be dismissed and have a new member brought in to replace them. Getting a new person up to speed is easier than having essentially no one working in the position.