3 of the 4 windows stopped working about a week apart. Fuses look ok but clicking sound from large pin relay under the back seat... Help

You are is already 20 year old. BMW's has electrical problems as they age. I've owned a few BMW's and every one has had electrical problems with the exception of the two 330i and 330ci. I've had a 2001 740il that had multiple problems with the windows. First it was the switch and then the window sensor. Get it checked by BMW or someone who knows what they are doing. I've always had BMWs even after have issues. Now, I just don't keep them longer than 3 years. My 740il has been a cash cow, but I really like the car and I feel it's worth the cost to keep it going. BMWs in general aren't cheap cars to keep longterm. I've had a Lexus that out last two 5 series, but I still continue to drive a BMW. They are worth the trouble and cost. When a car can put a smile on your face everyday, the cost isn't imporant.

Well, sounds like the relay needs replacing.

Take yr car to an qualified BMW auto electrial shop.it could be the relay or the motor.possible dried grese holding back.
check it out.