As far as "making" the kids dress alike-- I cut the Hart women a serious amount of slack on this, and don't feel we have enough information to make that a valid criticism, or imply it's part of a coercive lifestyle.
All the family photos released to the news are posed, from one of their trips to rallies, etc. Many families who never dress alike, will wear matching t-shirts to a family reunion, or a theme park, a festival, a cause like a breast cancer support marathon, etc. It's both a way to announce your "cause", and a way to quickly identify your group members. It's also a camaraderie thing.
These women have a lot to criticize about their parenting and behavior, IMO-- but matching t-shirts isn't something I can condemn.