Yes, I can see that too, but I think that Luke and Moira are "just" helping out with Nichole, seeing as they are the husband and best friend of the natural mother. But, of course, according to Gilead, June has no rights at all to Nichole and the child is Serena's, but it is ultra complicated.
It isn't exactly the same situation, but here is the Wiki article for foster care in Canada.
en.m.wikipedia.org/wiki/Foster_care_in_Canada
Foster children in Canada are known as permanent wards, (crown wards in Ontario).[1] A ward is someone, in this case a child, placed under protection of a legal guardian and are the legal responsibility of the government.
There are several different types of out-of-home placements or care arrangements:
Informal kinship: informal arrangement within extended family (ie.grandparent)
Kinship foster care: formal arrangement within extended family (ie.grandparent)
Family foster care(non-kinship): family-based care (family structure)
Group home placement: group living, 24h staff on duty
Residential/secure treatment: commonly referred to as "lock up", these homes are for children that need extra therapeutic treatment.
It appears as though the arrangement is along the lines of "informal kinship".