Tier 2 ICT to Tier 2 Skilled Worker - Dependent Visa change

Hi Guys, I am currently in the Tier 2 ICT Long term Visa category and have received an offer from a company with Tier 2 Skilled worker sponsorship. My dependants are in the PBS dependant category and have a valid visa for the next 2 years (as my ICT is valid for 2 more years).

1) Do they have to change their visa as Tier 2 Skilled Worker Visa Dependant or is this same as PBS dependant category and can continue for 2 more years and then change
2) If the answer to the above is YES they need to also change visa category, is it mandatory for them to apply along with me right now or can be done a month later as currently, they are in India. Note:- My new visa processing may start in few weeks.

Thanks in advance for all answers