pesachim 61

the slaughter and the sprinkling is valid if it is for those whose blood has been drawn as part of the covenant, even if they are in a group with those who haven't...

... yet

(performing the pesach sacrifice, people come together as a group. it is valid to do this for those who have not had a brit milah if there are those in the group who have. those who haven't could always get circumcised.)