Hi S....I totally relate!! I have four daughters and my husband travels. My oldest is away at college, so I deal with a 15, 6 & 5 year old. It can be REALLY exasperating! Some times I just wanna pull my hair out.
Like others have said, consistency is key. I admit, I've been inconsistent in the past and honestly it is terribly exasperating. The reason: When I am consistent, they consistently KNOW what's going to happen when the disobey. If I am inconsistent, they constantly push the limits to see how far they can go. It's human nature :)
Now I do NOT want to offend anyone here, because I used to go by the "three strike rule" and for me personally, all it taught my kids was, "well I KNOW I can do the wrong things AT LEAST twice before I get any consequences." Then the started getting creative....they'd get two stirkes in one bad behavior then move to another bad behavior for two more strikes and so on... Now, my girls know what I expect from them and they know, "first time, every time, obey". When I am consistent with that, it only takes a day or two for them to fall back in line...when I start slacking off, it only takes a day or two for them to push limits again. Being consistent is hard, because it's usually not convenient, but it's best for them and for you in the long run.
As far as types of discipline, you may have to play around with that for a while to see what's most effective. Could taking away T.V. time be most effective? Or sitting them in a time out in the corner? Or not letting them play with a friend for a day? Each kid has thier own personality and not all disciplines fit all kids. However, make sure the discipline fits the action. If one bites a sibling, for instance, taking away a toy may not be the best approach...perhaps saying, "well now you're going to have to do your sister's chores today because now she has a sore arm because you bit her". Be creative and make the "punishment fit the crime".
I don't know if you're involved in a mom's group, like mops. If not, maybe look for one. It's a great way to get out with other mom's while the kids play :)