Ok, this should be the right link for you.....
Legal Resources
This site is actually pretty easy to navigate around in......so you should bookmark it.
On the left, click the folder that says "Maryland Rules"
Then again on the left, click on either Title 2 or 3 (depending on what court your judgments are in) and then in the right window, you will see the different rules for process service.
And to answer your question on disputing - I would dispute the same (one) judgment with all 3 CRAs at the same time. Wait to get the results on those and then you can send in another round of disputes.