Pilot on a practice instrument approach reported a NMAC while descending into VNC airport.

Narrative

We were on an IFR Flight Plan and canceled IFR shortly before IAF to do a straight-in practicing approach into the runway that was used by everyone in the traffic pattern. Since change to advisory was approved by Approach control; we started to make our regular radio calls on the CTAF and listened to other calls on the frequency. Our own ADSB on the iPads as well as in the airplane showed (in addition to traffic in the pattern) one aircraft behind and above us approaching angular our straight in final approach course. We continued our descend and reduced our speed for horizontal separation. Neither I nor the safety pilot heard any additional radio calls than these of aircraft's in the pattern (no one said that they are on a straight in approach). As we further continued on our shown glidepath; we noticed that the aircraft behind us has turned onto the final approach course and is moving and descending faster than we are. The aircraft was approaching 400 ft. (shown on the ADSB) above and just slightly behind us; when the safety pilot made a radio call and tries to reach the aircraft. As no one responded he tried it a second time and got an answer that they are on the same frequency. The aircraft was directly above us (300 ft. shown on the ADSB) when the safety pilot informed them about the situation and asked for their intentions. They then started to do a right 360 degree turn to clear the situation. How the problem arose - aircraft approaching us without making radio calls. How it was discovered - ADSB inside aircraft and own one connected with iPads. Contributing factors - a lot of traffic in Venice (Many radio calls in the pattern); we had no visual contact because we had a Shoulder wing aircraft and the traffic was above (the other aircraft was regarding to Flightradar24 a low wing aircraft; so they maybe also did not have visual contact to us). Corrective actions - try to establish radio contact and aircraft making a 360. Perceptions/judgments - due to the aircraft being quite high and approach angular; we assumed that they will not do an approach into VNC.