Flight Instructor reported ATC failure to provide separation in traffic pattern resulted in evasive action and an NMAC situation.

Narrative

I was flying with a student and we had been cleared to take-off on runway XX at ZZZ. There was a flight of 2 experimental aircraft in the pattern. The tower reported they were on a 3.5 mile final when we were cleared for take-off. They reported us in sight. We did a short field take-off and as we climbed out the flight of two over flew the runway and were rapidly closing in on us; the Tower controller seeing how close they were told us to make an immediate left crosswind turn. (We were still over the airport) I took the controls and banked hard left; as I looked over my shoulder to my right; I saw the aircraft passing and now banking to the right. We were very close.Contributing to the event was the fact that the aircraft were going approx. 125 KPH; in the pattern; in formation. You can hear the controller telling me to turn left crosswind and one aircraft telling the other in a very stressed voice to 'break right break right break right'.We continued on the left downwind and did not have any other issues.This was the second issue that week with these aircraft flying formation in the pattern. On Day 0; they asked repeatedly for the pattern and the controller told them she was not comfortable. This was also at approximately XA:30 in the morning. This is a very busy time in the tower. Multiple airlines have departures and another flight school launches at least 5 training aircraft at that time of day. There is only one controller. I believe that formation flying in the pattern at ZZZ; an international airport; with multiple operations including military aircraft; several different airlines; corporate; and flight school traffic; is not a safe practice. Aircraft flying in formation have to manage coordinating with each other and with a busy controller. Experimental aircraft are an even larger risk since they may be doing flight testing.