Family of (Spouse and unmarried children under 21) of an H1 visa holder is eligible to get H-4 visas to live in US. There is no additional qualification required for H4 visa. The duration of H4 visa is the same as H1B visa of the principal.4 visa holders are not allowed work in US and are also not eligible to get a Social Security Number. H1 Visa holders can get drivers license and get and tax payer id for tax purpose. H4 visa holders can apply for other nonimmigrant such as the F-1 (student Visa).