The old after the fact tax queries.
To which Double Taxation Treaty are you referring? You need to look at any anti avoidance provisions for entities under common control which may or may be included in the Treaty.
Are the employment contracts concluded in Ireland, are there contractors with Irish Subcontractors concluded in Ireland? where was the variation in the terms of the building contract agreed?
A common convention
A person acting in a Contracting State on behalf of an enterprise of the other Contracting State - other than an agent of independent status to whom the provisions of paragraph (6) of this Article apply - shall be deemed to be a permanent establishment in the first-mentioned State if he has, and habitually exercises in that State, an authority to conclude contracts in the name of the enterprise, unless his activities are limited to the purchase of goods or merchandise for the enterprise.
International taxation is not my area but ten months and then transfer to a related Company is not the cleanest proposal I've ever seen.