Converting Wife and children onto my HSMP visa

[Alagomeji]

Hello All, I've been living in the UK for the past 4 years on an HSMP visa. While I've been here, I've gotten married and had two kids. At the moment, the kids hold the passports of their mother's native country, which is the USA. They however intend to travel this year to the states, and while they won't be disturbed while they're here, they'll definitely have some difficulty getting back into the country. Also, the wife's visa expires soon, so I'd like to convert her from a regular WP to an HSMP dependent. Can anyone please give me any pointers regarding how this can be done?

Thanks

[Alagomeji]

Just to explain properly - the wife is here on a WP that expires in september. Both of the children were born here in the UK (last year and this year, quite fast I know)