I can relate to this. Some students don't contribute to group work and even if they were my friends I have to say, I will try to include them in the group work and if they say no I will say "don't care about it" it's them they are failing in their grades not you. But sometimes u have to try a few times to get them to contribute in the group and then u got their attention for a few minutes. Though YOU CANT CHANGE THEM, it's their choice to contribute in the group work or not, NOT YOURS. Though dealing with it and with out putting your friends on the spot encourage them, and let them know you are there for them and you'll respect their decision and opinions for the group work. And ask others in the group to listen to him or her opinions. Hope this advice helps!