The pilot reported that, after exiting instrument meteorological conditions (IMC) during a circling approach, he was "a little above" normal glidepath and as the airplane crossed the approach end of the runway, the airplane began to sink rapidly and drift to the left. He added power to initiate a go around, but the airplane continued to sink, and landed with the left main landing gear off the left side of the runway. As the airplane became airborne again, he attempted to retract the landing gear, "but the handle was locked in place". He noticed that the left and right main landing gear extension lights were illuminated, but the nose landing gear light was not. The pilot noticed a positive rate of climb and decided to fly to an alternate airport. The pilot reported that, while en route to the alternate airport, a passenger reported that they smelled smoke, so he turned off electrical equipment. He utilized a pilot-rated passenger to assist with circuit breaker troubleshooting before turning on the battery again for communications. He instructed the pilot-rated passenger to visually examine the landing gear, who reported that the left main landing gear was extended without damage and the right main landing gear was "bent back", with damage to the right flap with fuel leaking from the wing. After contacting the alternate airport's tower, the pilot reported that he declared an emergency and provided a safety brief to the passengers. He added that, at the alternate airport, he performed an instrument landing system (ILS) approach and over the approach end of the runway, he reduced power, feathered the propellers, and moved both fuel levers to fuel cutoff. During landing, the right main landing gear collapsed, the right wing settled onto the runway, and the airplane began to pull to the right. The pilot added left rudder to maintain the runway centerline and the airplane came to rest on the runway. The airplane sustained substantial damage to the right wing. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.