Re: 3 tickets/3 days from Private enforcement company
Did you have the card in the window? If so, why would they have given you the tickets?
As for warnings, why should they? Any 'guest' would surely notice after the first one, I would have thought. And signs? Well, you don't say what part of the 'policy' you were breaching, but if it's in your block presumably the rules are available to you and you would be assumed to be aware of them.
Unless there is something else you're not telling us.
And yes, you should pay them, otherwise your friend whose car it is will be in trouble. Buying the car now will make no difference whatsoever.