How long does it takes to bring my wife & kids here in us as a immigrant ?

This is an immigration question, so I'll change the practice area. I would get the answer before you marry.

There is no way to know what the processing time will be. It always takes longer than you want it to! Once you marry (I presume overseas) you will have to file a petition for her and the case will go through processing in the US. Hire an attorney to help you get it right the first time so that there are no delays in your case. Thereafter if approved you will receive further instruction on what is required of your wife and her children in her home country to complete the process.

Generally, processing for a spouse of a USC takes anywhere from 12-14 months after initial I130, submission of supporting documents to NVC and scheduling of interview, although country specific for timing.