ATCT LCL CTLR TRIED TO SEQUENCE A SMALL MLT IN BETWEEN 2 MLT ACFT ON FINAL AND CAUSED AN NMAC.

Narrative

DUE TO DV MOVEMENT; ARPT OPS WERE CURTAILED FOR ABOUT 30 MINS. DURING THIS PERIOD; A FRONT CAME THROUGH PUSHING SHOWERS AND REQUIRING A RWY CHANGE. AT THIS LOCATION; RWY CHANGES REQUIRE FIRE TRUCKS TO ENTER BOTH ENDS OF BOTH RWYS TO CHANGE MAIA BARRIERS. AT TIME OF INCIDENT; MLT X HAD BEEN SENT AROUND FOR AN FGT WHO HAD NOT CLRED. ONE RWY WAS UNAVAILABLE FOR BARRIER CHANGE. MLT X ENTERED RIGHT CLOSED TFC TO FOLLOW AN MLT Z ON 4 MI LOW APCH FINAL. BEHIND THE MLT Z WAS MLT Y. AT THE TIME I MADE THE DECISION TO FOLLOW THE MLT Z WITH MLT X; THE GAP WAS ABOUT 6 MI. UNKNOWN TO ME; APCH CTL INSTRUCTED MLT Y TO MAINTAIN BEST POSSIBLE SPD ON FINAL; SO THE GAP EVAPORATED. I FORGOT TO TELL MLT X HE WAS TURNING INSIDE OF AN MLT Y (MY FIRST MISTAKE). WHEN MLT X TURNED BASE; I REALIZED MY PLAN WOULD NOT WORK AND I TOLD APCH TO TAKE THE MLT Y STRAIGHT AHEAD TO 1500' (MY SECOND MISTAKE) WITH THE INTENTION OF LNDG MLT X. MLT X WAS IN FACT ABOVE THE MLT Y AND WHEN MLT X SAW THE MLT Y; HE TURNED AWAY FROM THE RWY (AND TOWARD THE MLT Y) AND STARTED CLBING. MLT X WENT OVER THE TOP OF MLT Y. PER THEIR COMMENTS AT THE TIME; MLT Y AND MLT X SAW EACH OTHER AND WERE AVOIDING EACH OTHER. MLT Y RPTED SEP TO BE ABOUT 500'. I FEEL I WAS IN TOO BIG OF A HURRY TO GET THE MAIA CHANGES DONE. I SHOULD HAVE HELD ONTO MY RWYS UNTIL AFTER THE RUSH OF TFC THAT HAD BEEN HELD FOR THE DV MOVEMENTS (ONLY ABOUT 10-15 MINS).