Can a group of girls (11-14 years old) sing together in a nursing home?
If men will be present it is forbidden. See here (excerpt below).
From the age of 11, a girl may certainly not sing in front of men (or boys over 9). Some Rabbonim are of the opinion that even girls from the age of 6 should avoid singing in front of men. Some are careful even from age 3.
While there is a minority view that makes a distinction between a single girl singing and a group of girls singing, the general consensus in halacha is that no difference exists if it’s one girl or a group singing in front of a man.