Yes, I've put the multiport valve in an in-between position, opened the pump lid, and closed the valves on the suction lines. I'm confident water is not flowing thru the pump to the broken suction line.

I plugged the skimmers and wall drain with 1.5" threaded PVC plugs. The plugs fit tight, even if they are not a perfect seal, I can't imagine any leakage would be more than a trickle. But the water coming out of the broken line is a gush.

I have a vinyl liner, if I drain the pool level down below the skimmers, wall drain, and return jets that would have to stop the water flow to the broken suction line, right??