one thing that helps is getting them to know the difference from tattling and telling. if they are just telling you to get someone in trouble thats tattling and yoo could have a no tattling rule. However, if they are telling to keep someone from getting into trouble then thats a good time to tell. Does sound as if they are bored and spending too much time together. Do you have a new baby in the house? You said they were your older step children and they are only 4 and 5. If you have time kids almost always love to be read to. Also what are they doing wrong? Is it really wrong? Or are there too many ways to do something wrong in the house. Sounds as if they really want more attention since they get so much time with you while you are sorting it all out. It's tough on kids because doing the right thing for kids doesn't always get the attention that they need so they do something bad which gets our attention.
Good luck