General aviation pilot reported a near miss with two aircraft flying in formation opposite the traffic pattern at a non-towered airport in visual conditions. The pilot maneuvered their aircraft to avoid the other aircraft; then continued their flight.

Narrative

I departed VBT on Runway 36 at approximately XA:25 AM. The winds were 040 to 050 at 5kts clearly making 36 the active runway. Two other aircraft were in the area both broadcasting on CTAF 122.975 with intentions to land on 36.I announced on CTAF I was taking the active Runway 36 and departing the area to the north. Shortly after takeoff I heard on CTAF two Aircraft Y's calling out 'flight of two' inbound from the NW announcing intentions to land straight in on Runway 18. They clearly had not listened to AWOS (134.975) or monitored CTAF (122.975) or they would have understood that the active runway was 36. I was about ready to inform them that 36 was the active runway when another aircraft in the are broadcast that 36 was the active runway. I think I heard a response of 'OK…thanks;' but I am not 100% sure. I have a Aircraft X with a Garmin G1000 and ADS-B In/Out. I could see the Aircraft Y's inbound and watched them continue towards the numbers on 18. I began to move slightly east of a northbound course not knowing fully what the Aircraft Y's were going to do. My estimate of the closure rate was well in excess of 250 MPH! My Garmin G1000 audio warning was calling out 'Traffic; same altitude; less than one mile.' At that point I turned 90 left and began a quick descent only to see one of the Aircraft Y pass behind me with with 100-200 feet vertical separation and less than ½ mile horizontal separation. Way to close by any measure. I am not sure how close the two were in formation or if I saw the lead or number two plane.I continued to monitor CTAF and hear them begin calling out left downwind for 36; but was unsure if they were still a 'flight of two' or had changed to single ship. Either way only one plane announced left downwind and it wasn't until base turn that they both announced their position as single planes setting up to land. Again. In my 'qualified formation experience' neither of these pilots understand proper communication for flying in and approaching an uncontrolled airport in formation.I was taught and have always practiced making a 45 downwind entry into an uncontrolled airport to determine the traffic flow and observe runway conditions. I know nothing about the two pilots; but the approach they made by clearly not monitoring AWOS or CTAF; compounded by poor communication skills; were they a 'flight' or 'single ships;' made this an extremely dangerous situation.As I continued outbound I monitored CTAF until the Aircraft Y's landed. The post script to all of this is that an aircraft in the pattern called out to another plane in the pattern 'did you see that there were two Aircraft Y's not one.'Other than possibly changing course sooner than I did; I do not know what I could have done different; but I felt this situation needed to be documented as others may learn from it. In my opinion these pilots need additional training on communication skills and uncontrolled airport practices; but I also believe formation flying should require training and a logbook endorsement.