Assalamu-alaikum,
The only means of drawing one away from such a problem, is the reminder that:
"I may be alone, but MY ALLAH is watching me." and that
"Death can be approaching at any time.....even as I sit here before this screen".
Apart from being conscious of this, there is very little that is as strong a motivator, to stop one from engaging in something that is self-pleasuring and highly addictive.
If I was in this situation, I would do the following insha Allah:
1. Since he is using the family computer that is situated in the main room, it would not appear too unusual if you paste an ayat from Quraan on the wall directly above it:
e.g.
"He created the heavens and earth in truth and formed you and perfected your forms;
and to Him is the [final] destination.
He knows what is within the heavens and earth and knows what you conceal and what you declare.
And Allah is Knowing of that within the breasts." (64:3-4)
^ A reminder of our final return, and the fact that Allah is aware of our actions and thoughts - subhanAllah, all in one verse.
^^ It would probably be best not to include the arabic in this case (as one can not be sure if he will still continue watching such sites.....in which case, this would be the utmost disrespect to the words of Allah.)
2. Start sending him jumah messages - perhaps an ayat of quraan or a hadith, that again will return his remembrance to Allah and our final meeting with him, insha Allah.
3. Make it
your duty to find islamic talks/ courses, etc. in your area - and invite your entire family along. (You may need to nag - but thats ok - its for a good course insha Allah).
4. Download islamic lectures from dynamic speakers who address such issues, as well as other topics - e.g Nouman Ali Khan, Mufti Menk, etc......and play it loud enough for the whole family to hear and partake in its benefits. Maybe set a time each day, e.g between Asr and Maghrib - and make it a habit.
5. And as mentioned, make duaa that Allah pours His mercy upon your family and fills your home with the light of His deen.
It may not be possible to for
you to make your brother more spiritually inclined (for guidance comes from Allah (subhanawataála) - but it is possible to try and change the enviroment that surrounds him.
Every little action counts - do not doubt this.
It may be something really small and seemingly insignificant, that makes him realise the error in his ways.
May Allah grant us hidayat in finding a solution to rid our homes of this disease, that has been the cause of so many broken marriages and other unmentionable fitnahs.
Ameen.
:wa: