Sister, for your own spiritual development if nothing else you would be better to surround yourself with pious believers as friends. As you have said, these people are kuffar and as things stand are destined for a difficult time on the Day of Judgement as they have been told about Islam but have chosen to reject it...so far. Many of us will have gone through similar situations with past friends, but you need to distance yourself from this circle and find some new Muslimah friends who can help you get closer to Allah Subhana wa Ta'alaa.

You know best how to tell them, but unless you feel that there is hope that they are open to dawah then leave them behind for a better future for yourself in sha'Allah. If you do feel that they may be open to Islam then there are plenty of online resources to help you learn how to make dawah. Be especially wary at this time of the whisperings of the Shaytaan who will try and tell you they are good friendships to keep. May Allah make it easy for you to make the right choice.