Dependent children in Tier-1 Entrepreneur

i plan to apply for Tier-1 200000 route. one child will turn 18 in june 2018, other will be 16 in june 2018.
if i apply for Tier-1 in march 2018,
Q1- will my child who turns 18 in june we a dependant ? if so will she continue to be a 'dependent' after 3yrs and 4 months when i apply for extension. ofcourse assuming she stays with me and goes to college.
Q2- my other child will turn 18 during my stay i UK, will he also be considered 'dependant' after 3.4 years ?
Q3- can my spouse travel out of UK and take up a job overseas ? will it effect his eligibility when i apply for extension ?
Q4- will my son be able to get admission in state school as a UK resident under this visa ?
Q5- whats the current processing time for this visa ?

thanks.