because if they were marching against my socialist government, I may just join them.
Realistically, with an untrained militia, you can't engage them in a set piece battle. They have better training, leadership (more NCOs, jr. infantry officers), and weaponry (GPMG, mortars). Suggest harrassing to slow movement and interdiction of supplies (typical guerilla warfare). Perhaps even let them enter into part of the city and isolate them for the regulars to destroy. It worked at Stalingrad and in Buenos Aires (failed British Expedition during Napoleonic era).
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!