Polo Twist 2004 5 door Crash Senssors

Hello all,
I'm trying to sort out my niece's Polo that suffered flood damage. It failed MOT on airbag ECU Module and both side crash sensors. The guy who did the diagnostics (VCDS) said that I needed to get all three components from a single car. I found these from a breaker and fitted them. Unfortunately, the passenger side crash sensor gave a fault (I used VCDS Lite) and there was some evidence of corrosion around the metal reinforcing bushes on the mounting holes, suggesting that the sensor may have been water damaged.
Can anybody with experience in these matter please confirm whether: a) I need to start again and get three components from a single car; b) since the ECU Module and Driver Side Crash Sensor are OK, if I find and fit a a side crash sensor with identical part number, will it be recognised by the airbag module? c) if I buy a brand new crash sensor (anyone know the price?) will it be recognised by the airbag module?
I thought perhaps it was worth asking about a single replacement sensor as there seem to be a lot of single ones on offer on eBay.
I'd be most grateful for any advice that would let me help my niece.

go to VW Parts department & ask them

It should be on the computer that you need all 3

Getting genuine parts can be cheaper than you think, it doesn't cost anything to get a quote

as long as the part number is the same then it shouldnt matter where it comes from.