Detect the first rising edge of 3 input signals

You could use the circuit below with 3 D flip-flops and one 3-input AND gate. You would also need to use the reset input of the flip-flops to bring the output back to zero (not indicated in the schematic).

^{simulate this circuit – Schematic created using CircuitLab}

Put each input on the set of an SR latch, and AND all the outputs together.

As defined 3 rising edges are asynchronous thus reset 3 latches and NOR input= output