Yes. When Harry holds the ressurection stone Sirius is one of the people he ressurects. Sirius isn't fully alive but he isn't a ghost either.
Yes .
page 560.
After the fifth one the only time he appears is in Deathly Hallows is as a memory.
She was saying thank you for the toy broom he had sent to Harry
Yes, he returned when Harry held the resurrection stone and saw the spirits of his parents, Remus Lupin and Sirius.
None of four marauders were alive after Harry Potter and the Deathly Hallows. James Potter died before the first book, Sirius Black died in the fifth and both Remus Lupin and Peter Pettigrew died in the seventh.
harry potter and... the sorcerers stone, the chamber of secrets, the one with Sirius black, the goblet of fire, the order of the phoenix, the half blood prince, the deathly hallows
Although Dumbledore died in the Half-Blood Prince, he returns in the Deathly Hallows when after Voldemort kills Harry Potter, and comes to him, giving him a choice to "move on" or come back and fight.
The resurrection stone in Harry Potter and the Deathly Hallows is one of the three deathly hallows. If you hold it, you can see people that you love dearly that are dead and can talk to them. For example,when harry held it he saw his mother and father, Sirius Black, and Remus Lupin.
The initials in the fake locket say R.A.B. We find out in 'The Deathly Hallows' that R.A.B. turned out to be Sirius Black's brother Regulus, who no longer wanted to be a Death Eater.
Technically no, but in the deathly hallows a form of him appears to Harry before his confrontation with Voldemort. Thanks to the resurrection stone.
It didn't have a name, it was just named 'Toy Broomstick' in Lily Potter's letter to Sirius Black (The Deathly Hallows). Unless you mean his first real broomstick which is the Nimbus 2000.