would look look good for my sisters wedding?

Sounds good except for red tie. try a small stripe with light blues/darker blue -- tan because of brown shoes/no black. Yes dress khaki's are fine, well pressed, none of the just out of the dryer look. It's nice that you want to do this for your sister, she will be proud.

Match your tie to the shirt, blue somewhere in the tie. It is dressier.

It is dressier to wear grey, or better, black slacks, and black showes with those.

But, if you want the khakis or if money is a problem, go with a pair of ironed khakis.

for a neat clean look, match your socks to the khakis.

If it's not a formal wedding.

Darker pants would be more dress up.

Even if it is not a very fancy wedding, try to pick up a suit, even if it is just a very cheap one/second hand/discount stores/supermarket store suits

you are the brother.. and you should look different than others.. go for suit