Is it permissible for my maternal and paternal aunts' daughters to uncover themselves in front of me and to kiss me at occasions, now that I have become their maternal and paternal uncle through suckling?

It is permissible for one who has become a maternal or paternal uncle through breastfeeding to be in seclusion with the women who have become his mahram through breastfeeding. It is also permissible for them to appear before him with uncovered faces and what is customarily uncovered before mahrams. Similarly, it is permissible for him to kiss them, provided that there is no fear of fitnah (temptation) and no forbidden inclination. The more cautious approach is to refrain from kissing altogether.