When you say "self build", do you really mean appointing a builder yourself to carry out the build?
There are new Building Control Regulations in place currently which effectively put a stop to the traditional self build process.
Based on the above figures, I think you will struggle tbh.
Get out of existing house. Get the rental income started as the banks will allow a % of this onto your income.
Are your crèche fees on the bank statements? Can you pay them cash directly?
I don't know if the banks can see your credit union loans at present, some say they can, some say they can't, I know when I was in with PTSB last October chasing our second mortgage they couldn't see it.