This is always difficult. I guess there are a few things you could do. You could always talk one on one with the two clique ladies and discuss the situation and explain that it is not professional and could potentionally hold them back from progressing in their career path. Is there something the third lady is doing to isolate herself? If you think so, then perhaps speak with her as well and try your best to coach them. I would try to partner up one of the 2 with the 3rd lady to work on a project together and make them reliant on each other for various outcomes and the project's total success. Teamwork creates bonds. If nothing works, you need to communicate to them that even if they are not friends and do not like each other, the have to respect each other and be professional and that you will not tolerate anything less. Good Luck. Let me know how it goes.