No, it is not normal, well not usually. There do seem to be some kids that push the boundaries more than others. I totally understand that you want what is best for them and for them to be happy which is why you have to make a change right now! If they are running over you and "think everything you say is a joke" now, it will just get worse if you don't put a stop to it. Have you ever seen the show Nanny 911? There are a couple of other ones that are on that are similar and have really good advice. Most of the kids on there I think are younger but the lack of respect is the same. That is what is wrong with our society, too many parents don't want to come down on their kids and as a result let them get away with things and then as they get older they want to get away with more and it gives them a distorted view of reality when they get out on their own.
You are their mom, the head of the house and the person that loves them the most in this world. Sit them down, tell them that and then tell them that things are going to change. If it is too hard to do that with them together then do it individually. Keep your cool and tell them that they will respect you, they will obey the house rules and there will be consequences for when they do wrong. The most important thing to do is FOLLOW THROUGH! Do it in love, but when they have broken a rule or dispected you then take away a priviledge (their phone, computer time, tv, going to a friend's house, etc.). If they think you are "just talking" then when they are withheld something they want to do, they will understand you mean business - as long as you follow through -everytime. My daughter had a birthday party and 2 of the guests were sisters. Well, the mom came with one of the girls and said the other one was not allowed to come because she had been dispectful to her and mean to the other sister. She gave her a warning and when she still refused to "straighten up" and continued her bad behavior the mom said as hard as it was, she had to follow through and not let her come to the party. Of course the girl had a total fit and was very upset but if the mom would have given in then there would have been no lesson learned.
As far as the telling on each other...one of my daughter's teachers had a rule in her classroom - if it didn't have to do with blood, a flood or fire - she didn't want to hear about it! Our version at home however was if it isn't Kind, if it isn't Necessary or if it isn't True - don't say it. You can put this on a paper and put it on your refridgerator and just point to it when you get tired of repeating it for the hundreth time! It is really a good way to get their attention actually - just memorize that short rule and repeat it over and over. If they don't listen the first time, say it again, if they still continue with tattling, say it again. If they say "mom, quit saying that!!" say it again. They will get the point and it saves you from having to try to be the referee.
Stay strong and know that giving them boundaries is the best thing you can do for them!
Just remember - you are the adult - you have the authority in the home, not the kids. They need to learn to respect authority for their sake as well as yours! Do it in love and always follow through. It may take awhile but it will work.