Offline transfer contacts and text messages from Android to iPhone
Apple publishes an app on the google play store that you could download to the android and then try running the transfer from a network that has nointernet connection to be sure it’s not using cloud based transfer. 


https://support.apple.com/en-us/HT201196


I suppose that’s third party software from Android point of view but it seems pretty first party of you are ok with macOS and iOS. In fact, one of the troubleshooting steps is to disable cellular network which makes me think it uses local network discovery and intentionally doesn’t want your data going anywhere except from one Android device to one iOS device. (That also follows Apple’s long time design to never send data out when you can keep it local.) 

If you have closed WiFi, use that and you don’t need the Mac. The only case I see needing Mac in this scenario is if you want to use the WiFi hardware to make a local network for both mobile devices to talk to each other.