"Putting on Social Security Employee hat-- remember I am not an expert and this is not considered a "benefits counseling" session
Now that is out of the way--
1) There are different types of of retirement. The first thing you need to know if the true Full Retirement Age (FRA). In some cases, depending on your birthday, most peoples FRA is AFTER age 62. Some people it is 65 and 4 months, 65 and 6 months, etc. In some cases, it is 67.
Here's the law:
https://secure.ssa.gov/apps10/poms.nsf/lnx/0300615003
2) If you pick reduced benefits-- you will stay reduced. The rule is pretty much once reduced, stay reduced type of thing. Of course there are exceptions.
3) An "offset" of benefits may occur if the claimant if the person is receiving different benefits, such as a government pension, unemployement. Of course this is a state by state basis, but many states are no longer offsetting retirement claims.
4) Another thing to think about is the day of the month your sibling was born. If they were born on the first or the second of the month they will be entitled to benefits for that month if they are born on any other day of the month, they will get benefits the following month.
Say your birthday is 04/08 you will not get benefits until the following month.
5) The website has some great resources for applying for benefits. You can always go online to apply for retirement benefits or you can call the 800 number and do it over the phone. The 800 reps are really knoweledegable.
http://www.ssa.gov/retire2/applying8.htm
If you go the 800 number route, ask the rep the following questions:
1) What will be reduced benefit be?
2) Will my unemployment checks be offset?
3) Can you tell me how much my retirement claim would be if I waited for full retirement age?