The gas smell is obviosuly more of a worry as far as safety goes and as said you can report him for that!
The rest of it though is just shoddy work which sadly you can only sort out with him really so just politely tell him there won't be any cash till you're happy......i'm an electrician not a plumber but the amount of other tradesmen you go in behind to sort out their mess is surprising really, it's as if some people just have lower standards than others and can't see what's wrong
Being a friend of the family doesn't help either does it, how exactly is he reacting when you tell him what you think of his work?