As per this article (Dirshu), it must be done in front of three men, even if the person that had the dream was a woman.
As per this answer (Rav Yuval Cherlow), it is preferred to do it with members of your gender.
According to this article, family members may be used (Rav Moshe Shternbuch in the name of the Brisker Rav). This would likely help many people find three people who care for them more easily, and not necessarily need to use less than ideal "friends".
I have not found anyone who addresses a non-Jew taking part in a Hatavas Chalom. The non-Jew would be saying a number of Pesukim and/or blessings that are part of the Hatavas Chalom, which seems a bit weird, but is likely not prohibited. Also, based on my (very minimal) experience, people tend to simply choose three people that are present when they daven Shacharis in the morning.
(There might be some Halachic issues with being a particularly close friend with a non-Jew in general, but here is not the place to discuss that.)
Also, note that the Talmud (Berachos 55b) does not mention that they must specifically be friends, although Shulchan Aruch (OC 220) does.
Obviously in any specific case, a Rabbi should be consulted.