Answer:
This is what I will apply.
A- I would first check if the wireless connection is using the fastest wireless standard the router supports, and if it is I would then
D - this will enable QoS for the gaming application on the router and on the son's computer. However, if that is not enough and wired cabling is feasible
C - I would then recommend using wired Gigabit Ethernet connection from the router to the son's computer.