Female cousins and daughters of one's female cousins are non-Mahrams (not a spouse or an unmarriageable relative) for their male cousins. Their uncle's marriage of their mother or the girls' serving of their male cousins does not permit the boys to look at their female cousins or the daughters of their female cousins. It is also not permissible for the girls to show their faces before their male cousins. (Part No. 17; Page No. 431) But it is permissible for the boys to marry their female cousins or the daughter of their female cousins because they are Ajanib (men other than a husband or permanently unmarriageable male relatives) to each other. It is also permissible for the male cousins to visit their female cousins without being alone in seclusion with them. Moreover, the female cousins have to wear Hijab (veil) and legal proper clothes before their male cousins. The mother and father will be sinners if they permit their daughters to uncover their faces or appear in legally improper clothes before their male cousins. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.