Officially you will need to submit the songs to MCPS for a license. They will ask for the publishing royalty upfront (8.5% of the published dealer price).
If the songs are all traditional then you will be OK. Check for some other versions of them - they will have Trad, arranged by xxxx instead of a writer's credit. Otherwise, if the writer has been dead for over 100 years the song will have become public domain.
I'd guess a lot of acts do ignore the process. MCPS get reports from CD manufacturers, in fact, the manufacturers should not produce the CDs unless a license is in place. If you are running them off yourself or getting CDRs replicated in small quantities then these will not be reported. Chances of MCPS finding out? Probably quite low, but, like HMRC, they are a tenacious bunch.