There is no Neturei Karta dress code:
Each member dresses according to his custom or preference. That being said, many are very religious and seek a old fashioned outwards appearance. Therefore, many will e.g. opt for a flat shtreimel without "crown".
The graybearded man is a Hirsch1. He is anti-chassidic litvish, and wears the traditional clothes of the Vilna Gaon's fervent followers. Their breeches are not tied (or velcroed) tight around the knee highs like chassidim's are, they have regular laced shoes, as opposed to chassidic "ballet flats", and regular dress shirts, as opposed to chassidic ones.
R' Moshe Ber Beck wears white knitted pom-pom skullcap with kaftan and vest that is blue with white stripes on weekdays, and gold with blue stripes on Shabbos. All in accordance with the dress code of Toldos Aharon. Noticeably, he does not wear pants, only the traditional knee-long chassidic underwear.2
I don't know these two men, but they seem to wear the traditional dress of Toldos Avrohom Yitzchok, black with white stripes.
The most noticeable "members of Neturei Karta" are followers of R' Beck, who was a Wiznitzer chassid. R' Beck was upset by the Zionist tendencies of the future Wiznitzer Rebbe, R' Menachem Mendel Hager3, and created a splinter group. Some families from the traditionally quietly anti-Zionist, non-chassidic old yishuv, notably the Hirsch family, joined forces with R' Beck and brought their customary Old-Yishuv title, Neturei Karta, "Guardians of the City", with them.
The Beck-Hirsch Neturei Karta is not a coherent group, and the only requirement of its members is anti-Zionism. Many people from all kinds of groups and backgrounds, consider themselves affiliated, which does not preclude their membership in other groups. In their synagogues and at demonstrations, one will therefore see many types of clothing.
I know many of these people, and have been to their homes, synagogues, and demonstrations. I discussed clothing with several.
1. I was in his home in Meah Shearim once, but I cannot recall his first name right now. Will edit if I remember.
2. Similar to Mormon underwear, without special symbols.
3. At the time, it was not conceivable that the anti-Zionist R' Yisroel would become Rebbe.