Hi I moved here in Feb 2017 on H1B and I have below questions regarding tax benefits for my H4 dependents.

1.When I file tax for year 2017 in 2018 how much tax benefit I will get if my dependents are with me during filing day but not in US in 2017?

2.Do my dependents have to be in US for more than 180 days to claim the tax benefits?

3.How much benefit I get for each dependents if they meet all required criteria to claim?

Thanks in advance.