wir means we not me ....... thus being said the first line of the song would either be
wir marschieren richten in das Schlachtfeld
OR
Wir marschierte richten in das Schlachtfeld
OR
wir marschierte in auf das schlachtfeld
There are a lot of ways to write it
And the first line also says this
Wir zogen in das Feld.
Meaning we moved into the field
Finally their misery ends, because when lansquenets came to their battle they got the chance of being paid or to plunder.
Thanks to user Alsweider for information on Siebentod and the Landsknechtwelsch (I also found it was old Spanisch) part.