How to convert your dependent visa after main sponsor passing.

Hello Everyone,
My cousin came into the UK via the tier 2 healthcare worker route. He had 2 dependants, a 15 year old son and wife. Now they want to know what happens to them and their visas. What do they need to do to ensure they remain, do they need to find a way to remain or there wont be any problem with them using the remaining 2 years of their 3 year visa.
Also the biological mother of the child is in America, How does the Mum apply to take the child to her in the states?
I dont really know how to advise them.

The spouse needs to find a visa they qualify for. No rhe dependents cannot simply continue staying in the uk on their dependent visas if the main visa holder has passed.

If the child's mother is in the USA, it depends what her immigration status is to take the child back on a visa