Must cousins—the older aged 16 and the other 15—wear hijab in front of their 19-year-old male cousin who lives with them in the same room?

A man's female cousins (daughters of maternal or paternal aunts) are considered non-mahram to him, and it is permissible to marry them. They are obligated to cover their adornments and not remove their hijab in his presence, based on the Almighty's saying: "And tell the believing women to lower their gaze and guard their private parts and not display their adornment except that which [ordinarily] appears thereof." It is not permissible for a man to reside with them in the same room. It is not lawful for a man to reside in a dwelling where there is a non-mahram woman unless the dwelling is spacious and the man occupies an independent part of it with his facilities, such that the causes of fitna (temptation) are removed.