MLG ACFT ON APCH TO SJC HAD SMA ACFT ON PARALLEL RWY APCHS. 2 PARALLEL RWYS WITH ACFT IN PATTERN; ONE EITHER SIDE OF RPTR; THE ACFT TO RPTR'S L OVERSHOT CTRLINE AND FLEW UNDER RPTR ON ILS APCH. EVASIVE ACTION WAS TAKEN IN ACCORDANCE WITH TCASII RA.

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ON SHORT FINAL TO SJC ARPT; WHILE WITH TWR; WE WERE CONFIGURED TO LAND ON RWY 30L. AT LEAST 2 LIGHT ACFT WERE TO OUR R ON RWY 30R MAKING PATTERNS THAT CAUSED TFC ALERTS BTWN 2000 FT AND 1000 FT ON ILS GS AND CTRLINE. BOTH WERE SEEN AND VISUALLY IDENTED. AT THIS TIME OF DAY THE SUN WAS LOW IN OUR FACE CAUSING REDUCED VISIBILITY; PARTICULARLY TO OUR L; WHICH WAS DIRECTLY INTO THE SUN AND HAZE. THE TWR ALSO ISSUED TFC OF A PIPER MALIBU TO OUR L FOR RWY 29. WE NEVER SAW HIM BUT THE TWR RPTED TO US THAT HE HAD US IN SIGHT. HOWEVER; THE MALIBU ENDED UP UNDERNEATH US AS WE WERE DSNDING ON GS AND CTRLINE (ILS). OUR TCASII TOLD US TO MONITOR VERT SPD AND WE SLOWED OUR DSCNT. TCASII THEN SAID CLB AND WE COMPLIED. DURING THESE WARNINGS; I WAS LOOKING FOR THE MALIBU AND AS I STARTED CLBING I FOUND HIM TO MY L AND STRAIGHT DOWN; SEEING ONLY THE TOP OF THE MALIBU. TCASII SHOWED 100 FT SEPARATION. THE MALIBU STARTED MOVING L; BACK TOWARD THE CTRLINE OF RWY 29. THE TCASII RA STOPPED AND WE CONTINUED THE APCH TO LAND. WE TOLD THE TWR HE WAS TOO CLOSE; TWICE; AFTER SEEING HIM. THIS WAS AFTER WE WERE CLR ENOUGH TO CONTINUE THE APCH. I BELIEVE THE TWR; WITH TFC ON BOTH SIDES OF US; SHOULD NOT ALLOW A SMALL PLANE TO TURN BASE INTO OUR FINAL APCH; BUT SHOULD EXTEND DOWNWIND TO AVOID CONFLICTS SUCH AS OVERSHOOTING. SNA ARPT MADE A SIMILAR CHANGE AND SJC IS EVEN MORE CONGESTED WITH TFC ON 3 RWYS. BETTER POSITIVE VFR SEPARATION NEEDED.