Let me explain better and if you are this boy parents would you let him do that?
The boy is vacationing with his dad, his sister and other family members he has (his aunts and his cousins ) and he took his girlfriend with him. He was the only family member who took his girlfriend to vacation with him as he told his dad that he will go on this trip only if he can take his girlfriend, if he could not go with the girlfriend, he won't vacation with him, so his dad accepted (stupid the father is, by not having "pants" to tell his son he could not take his girlfriend). The other cousins also have bfs/gfs but neither one took them with them, cause their respective parents did not allow them to do so. Anyway, you probably will think that this man/boy was going to sleep in the same room with his father (man with man in the same room) and this boy sister was going to sleep in another room with her sister in law (woman with woman) but no, the boy wanted and insisted to sleep in the same room with his girlfriend, with one bed (no separate beds in the same room). This plan was already organized before leaving for vacation and meet the family days later. Not only that but the boys father even covered all the expenses of the sons girlfriend, cause the son wanted his dad to pay the expenses of his girlfriend. The girlfriend did not pay anything, she just went for free literally. What a stupid father!!
So at the end, the boy slept with his girlfriend and the boy`s sister slept with her dad (separate beds of course). That means the father did not say anything his son sleeping with the girlfriend. This boy
This boy had always been a mischievous man, always like to get away with it and do whatever he wants even before being 19yrs old. Now that he is 19yrd he believes as he is already an adult and legal age he can still do whatever he wants, even if he still lives with his father and his father continues to pay his studies.
My opinion is that this boys behavior was a little disrespectful toward this boy family