You'd need to first add weapons to village walkers, and make sure that unarmed versions are set as the faction's town_walkers.
Code:
(store_faction_of_party, ":fac", ":village_no"),
(faction_get_slot, ":reinforcement", ":fac", slot_faction_reinforcements_a), #get faction templates
(faction_get_slot, ":villager", ":fac", slot_faction_village_walker_male_troop), #male defenders only
(try_begin),
(party_get_num_companions, ":party_size", ":village_no"),
(lt, ":party_size", ":ideal_size"),
(party_add_template, ":village_no", "pt_village_defenders"),
(party_add_template, ":village_no", ":reinforcement"),
(party_add_members, ":village_no", ":villager", 5),#arbitrary amount
(try_end),