I'm in the US on F-1 visa. but my mum has an immigration case with approval 797c. can I use this 797c for green card application

If your mum immigrates to the US, there may be a chance for you to immigrate along side with her as her dependent.

Are I-751 interviews more frequent?

Many cases are scheduled for an interview. if you are concerned, you should consult an attorney to identify any red flags that may have triggered...

Need help with brothers deporttaion.has been depoted one wonse .

If he has already been deported once and was imprisoned for illegal reentry, his prior deportation will be reinstated.

K1 visa or permanent resident status in canada

This question lacks any foundation to allow an attorney to answer it.

I'm confused If I already applied for 1-485 do I need to apply for 1-130 or only if I need to petition my relatives . ?

This depends fundamentally on who you are petitioning and where they are. You should probably consult with an attorney.

Probably not, under those circumstances.

Entering U.S twice in a year

Yes, returning o the US too frequently on a visitor visa can arouse suspicion that the traveler is an intending immigrant.

Work on L2 visa with EAD renewal receipt?

You should have a valid EAD in order to work. These are issued in 2-year increments, so the request for extension should have been filed well in...

I would like to file for a B1 Visa extension for 2 months, Do I need a an I-135

I believe you are referring to an I-134. Please check out the instructions at www.uscis.gov.

Can I fill up ds 260 for my wife and kids

You should be able to accomplish that via the internet.