He is a friend of Jack's mother
It is not common but if she cares for you and you and your friend are very close it won't hurt to give her a happy mothers day card as a friend.
Mothers will generally hide them at their work or a friend's house where you have no access.
If mother is singular: mother's If mother is plural: mothers'
Mothers is more than one mother. Mother's is something that belongs to a mother. "The mothers group is meeting Tuesday." "My mother's car is in the shop."
You would use "mothers" for two, as it is a plural noun.
Mother's with the ( ' ) of course shows possession.So you could put; "My mother's friend came for tea today.Remember, mother's without the ( ' ) only shows plural.
The plural is mothers-in-law. (not mother-in-laws)
The possessive form for the plural noun mothers is mothers'.Example: The mothers of several students have formed a mothers' committee.
The difference is the placement of the apostrophe. "Mother's" with an apostrophe before the "s" is possessive, indicating something belonging to one mother, whereas "mothers'" with an apostrophe after the "s" is possessive, indicating something belonging to multiple mothers.
The plural of the noun mother (female parent) is mothers.
The plural form for the noun mother is mothers. The plural possessive form is mothers'.Example: The mothers of several students have formed a mothers' committee.
Your mother's mother would be your grandmother.