The best choices for your attendants are best friends and close relatives. The number of these is completely dependent on your opinion and wishes. The average formal and semiformal wedding includes four to six bridesmaids.
Informal weddings vary much more and can simply involve a maid of honor and ushers.
You also have the option of having a flower girl and a ring bearer. Involve the children in the wedding in some capacity, particularly as attendants, if they are old enough. Discuss this with your first spouse so as to avoid any awkwardness for the children. When you choose, make sure that this person will be helpful. You will need to depend on this person for lots of assistance and support.