The woman died from her gunshot wound, while the 66-year-old was taken to hospital in a serious but stable condition.
Police were called after 4.30pm and made an emergency declaration and put an exclusion zone in place at 5.20pm.
Patrols later found a suspect vehicle and about 7.45pm arrested the 31-year-old man outside a fast-food restaurant about 2km away from the shooting scene.
He was assisting police on Wednesday night.
“I don’t have any details at this stage in relation to any sort of motive or reasons behind what’s occurred,” Paine said.
Police did not know if the woman and two men were known to each other but believed they “resided in close proximity to each other”.
Paine said police were examining a number of scenes.
The shootings were “an absolutely shocking thing” for the teens to have experienced.
“They obviously were very fearful and they’ve gone and sought help and that help was provided and unfortunately that male who also provided help has been injured, so an absolutely tragic situation,” Paine said.
The emergency declaration was revoked around Robb Place, Paradise Street, Archibald Street, Kindermar Street and Denton Street.