H4 visa requirements for stepchild from India

[rahulnhelp]

Hi, I am on H1B for more than 10 years in US. My wife (on H4) passed away earlier this year battling cancer. I have a son who is a US Citizen.

I am planning to remarry someone (divorcee) from India who has a child from her first marriage. What will I need to do to sponsor H4 for the stepchild? Do I need to adopt him in India after I marry her mom?
Any advice is helpful here.

Thanks!