alternatively if you mean "mario and luigi" as in the rpg series, you can either create a fork of smrpg: the seven sages (an open source game made in rpg maker which is even easier to use than gms2) or perhaps a romhack of superstar saga using
yoshi magic (though i'd discourage the latter if you have no prior experience in romhacking)
to my knowledge however, there exists no readily available engine for this purpose written in gml.