.Jhapali Babu,
if you are confident that you can fill out few simple forms yourself, you dont need any lawyers.
download Instructions and form I130.

This is very simple process and should not take long for you (being a US citizen). Processing time may vary depending upon ur relationship with your family member.

You have to file that I130 for each of your family members and wait. Once those petitions are approved, USCIS will notify you. And once Visa numbers are made available for your beneficiary, they can go to consular's office in KTM and apply for Immigrant Visa.

As I am not an immigration expert, do more research .... you don't need lawyers for this process, but if you want need information, just get appointment with one of them for consultation. Many lawyers give free appointment for first consultaion. Make sure you get as much information as you can, on your first visit.

Good Luck