We had guests in January who'd done a Big Island day tour that included Volcanoes park. It's really spectacular, but to do it as a day trip/tour, plan on a 12- or 16-hour day with flights (and airport waits). I think you can book tours from Oahu (flight to BI + bus tour that includes Volcanoes and other sites), but the flight from Maui would be much quicker. Ask the concierge at your hotel -- the details change all the time. (Probably about $300/person.)
I doubt that a tour would get you down to the flowing lava because of time constraints and safety concerns. For that, you'd probably need to book a flight to Hilo and rent a car to get to the park. Access to the flowing lava is monitored carefully by the National Park Service. The most recent vent has been spewing sulphur dioxide, and the whole park has been closed for a few days recently because of the fumes. (There were a few days on Maui in May when we couldn't see the Lana`i or Moloka`i from our house because of the vog, or clouds of sulphur dioxide.)
The link for the park is
Hawai'i Volcanoes National Park - Kilauea Volcano Status (U.S. National Park Service)
The US Geological Survey keeps a page of Kilauea's current status at
HVO Kilauea Status Page
and there is more general information about the Hawaii Volcanoes Observatory from the USGS (including photos) at
HVO Kilauea Status Page
There used to be great helicopter flyover tours from Maui, but I don't think they do them anymore. Then for a time there were small-jet flyover tours from Kapalua airport. Your concierge should be able to help; you will not lack for people trying to sell you "activities," for sure.