My god sons new house!

As far as I know the answer is no on both counts.  I doubt there are any grants available unless the house is in a centro storico and there is local money available to preserve the facades etc.  Re septic tanks - it may be a local requirement - perhaps to separate the black from grey (recyclable) water - but its not something Ive ever heard of.  Your best bet is to have a response from someone local.    

I'm in Emilia Romagna and we only have one, think the builder is trying to get more money out of them. Surely the kitchen water dilutes the bathroom waste which stops the tank getting bunged up. I would talk to geometre as well as some locals and if the geometre agrees with the builder then ask him for the reason. It's their house and they shouldn't agree to anything unless there is a justified reason, chances are it's just a scam and often geometres and builders are in it together. You really need to stay in control of any 'extras' they decide you need or you will end up spending money uneccessarily. If in doubt ask another geometre/builder.

If in doubt - ask the Comune

Alan H beat me to it! I too would speak to the comune - they will give you the official and independent line - planning permission may be required so best to involve them early on.

The Ufficio Igiene rules on septic tanks fosse imhoff and not technically the comune.  SO it would better to enquire at the Province.