so is the problem the platform, because it does not for consoles?
Splitscreen shooter games for pc are extremely rare.
You are asking for splitscreen in the forum of a game that is a PC exclusive, that does not and will not support splitscreen.
So please understand why some replies are not sure if they can take you seriously.
For having a great time playing videogames with you brother, I recommend the following.
1- stick with consoles.
2- Find something better than a 12" black and white tv as mentioned in your other thread. If you can afford a computer with internet, you can get a respectable tv... Any old big CRT TV's are practically free ! (Advice, make sure it takes Component (Ypbpr) or the single component video, or svideo
Now for console advice... PS2 is decent... But if you really want to have fun for not much money...
Find yourself an Xbox or an Xbox360
You can research Softmod, Xbox Softmod... XBMC, Xbox Mod chips...
Your goal is to get all retro consoles (Super nintendo, sega, n64, neogeo) in your Xbox...
1- it's a great learning experience. The reading will help your English
2- You will become more of a tech, you will learn a lot
3- the reward is endless hours of classic gaming with your brother.
Stop asking a specific game's forum why the game isn't splitscreen when you can't really share a mouse or play without it... it's just crazy.