As I understand it you seem to simply have a way of sharing the costs among you. You aren't 'renting' to third parties, and aren't seeking to make a profit. All you are trying to do is find a way to share the real costs among the three of you.
I'm no expert in UK Corp Tax, but would be really surprised if the HMRC would seek to tax any excess income on this. Certainly the Irish authorities would not.
There doesn't appear to be any "trade". This is solely a cost allocation vehicle. Presumably if you continue to make a surplus, and the anticipated contingent expenses never arise, you will amend the rates to reflect that.
If there is no trade, I can't see how it would be liable to UK CT, but as I said I'm not an expert on UK CT.
There are some here who are more familiar with UK CT and will probably comment for you
dp