Going by the book, you should be submitting income tax returns in both Spain and Ireland. As a PAYE employee, you should submit a Form 12 in Ireland and should receive credit for any income tax paid in Spain under the relevant double taxation agreement.
There are different rules in different jurisdictions for calculating rental income. For example, in Portugal you don't get a deduction for mortgage interest. Agents fees and insurance should be deductible in Ireland and I suspect the same should be the case in Spain. However, you should get advice from a expert in Spanish taxation. I have seen Irish companies advertising online that offer advice in relation to the submission of Spanish/Portuguese tax returns for (say) €250 + VAT per return. That's just a casual observation and not a recommendation.