My father-in-law has a Macaw that is aggressive toward anybody but him. He has to go out of town and asked if me and my hubby would take care of it. Is there a way to calm the bird so it won't bite us. I don't know anything about birds.

That is the nature of that kind of bird. They are usually one-man birds. He's gonna freak when your father-in-law leaves. Poor little guy.

If he won't be out of town long and it has a large cage, it might be best to leave it in the cage and not stress the bird anymore than it will be to have it's owner gone. If the bird isn't hand raised , and it sounds like it wasn't if it is so aggressive, I wouldn't wear gloves around it. Parrots have amazing memories, as befits birds that live for decades. Almost all parrots gotten from the wild have been handled very roughly by men wearing gloves. It makes many parrots more aggressive and protective of themselves. They bite harder with a gloved hand and you really need THICK gloves to not be injured by a macaw bite.

Can I suggest that if you need to approach the bird you do so with a closed tight fist with your hand curled against your wrist. It is the least aggressive and safest way to approach strange or aggressive birds. With this tight fist you can actually move the bird or direct it where you want to go. Much better than any glove. There is really no quick way to calm down an aggressive bird. Think positive calm thoughts, imagine you are the bigger bird. Try to keep him below your eye level and use the tight fist and hopefully you can get through this okay:-)

my mom has and african-gray parrot that is only nice to her. so when i go to hold it i have to put on a leather glove so that when it bits it dont hurt and it cant bit through it. after a while of holding the bird it gets to be nicer. but the more you hold it the nicer it will be towards you.

Don't get close enough to get bit, if you can help it. I would suggest keeping the cage in a quiet corner of the house, and cover it at least 8 - 10 hours every night. There are probably professional bird sitters, if you want to hire someone. Here's a link to a bird care site:
http://www.multiscope.com/hotspot/care1.htm