expiration date for B2 visa

[myvisitors]

My parents and sister is visiting me in August 2007, I have 2 questions regarding that
1. They have got a visa appointment in April, if they get single entry is it too early? what is the usual expiration date?
2. Can they all use the same docs like bank statements, pay stubs(My sis and my parents have got different appt. time)?

Thanks a lot in advance!