Toadfrog,

Ein Heller und ein Batzen: also known and sung by others than soldiers, especially students in the 19th century; the tune used nowadays adapted to marching by usage of the troops.
Erika: A product of WW II, composed by Harm Niels, a then famous composer of popular songs. Unfortunately I lost the song book with this song when I stopped practizing the accordion.
Westerwald: not traditional, also a marching song written and composed in WW II or shortly before.
Maruschka: There is a short student ditty containing this name, but this can't be it. I don't know another song; since you say it shouldn't be sung to a Pole: could it be the song beginning in einem Polenstädtchen (in a little Polish town ther lived a girl)?
Maerkische Heide: It not only does sound innocent enough, it is. It is the unofficial anthem of Brandenburg, heart of former Prussia. I found the song with the writer's name, G. Büchsenschütz, but no year. Since it is copyrighted by a Berlin musical publisher I assume that it was written in the 20th century. You won't find any bad ideas in it other than love to the beauties of your home country. [Note: The R at the end of Maerkischer must be omitted]

Wilfried