Coach Tom Coughlin says “I want ’em all’’ when asked about his own free agents but acknowledges that’s not going to happen. How much the Giants have to spend depends on their salary cap situation, which is directly tied to a pair of veterans, cornerback Corey Webster and offensive lineman David Diehl. Both players are coming off poor seasons entering the final year of their contracts. Both started in Super Bowl XLII and again in Super Bowl XLVI, but their returns to the Giants are not guaranteed. Webster’s salary for the upcoming season is $7 million and he’s scheduled to count $9.8 million against the cap. Diehl, 32, is scheduled to make $4.475 million in salary and his cap hit is around $6.9 million. It is virtually impossible for the Giants to bring Webster, 31, and Diehl back at their present salaries. Coughlin steers clear of money issues, but said he wants both players to return for the 2013 season. “I do,’’ Coughlin yesterday told The Post before a signing at Barnes and Noble on Fifth Avenue for “Earn The Right To Win,’’ his new book. “I think there’s no doubt they can definitely help the team. I do want them back. They can still contribute.’’