Is this a reference to the Thomas Batt you are interested in? I think he was a Director of the Belfast Banking company (nowadays the Danske Bank!).
Robert Thompson] on board the [schooner] "Magician". Journal of his tour to Constantinople - describing the various ports and towns visited. "The Magician" left the Princes Dock this day at 3 o'clock ....." Arrived at Cadiz 2nd April where he was confined on board to fulfil quarantine regulations until 6th April when "we have taken our tickets by steamer to Seville" he returned to Cadiz on 10th and left the following day for Gibraltar where he stayed from 12th-14th then to Algiers 19th-22nd and Malta 25th-28th where he left the Magician and booked "a passage to Constantinople ......" after some difficulty got berths on "the Erskine" landing at Gallipoli on 2nd May" on our landing never could imagined anything so very bad, the shops, houses, shops and people are the worst I could have imagined we went as far as the French Camp where they appeared much cleaner and better than those in the town ......" Arrived at Constantinople 3rd May, "many large English steamers here, the Golden Fleece, Kangaroo, Emeu .... when we landed ..... we went to Missiries Hotel, which we were told was the only one English people could go to, only one room to be had and I went to a room provided by the hotel in a private lodging house ..... well furnished and clean ......" Describes the town of Constantinople "we ordered three horses and started with our guide to ride round the Ancient Wall of the City ....." on the 11th May "went over to Scutari to visit some of our friends in the camp ..... called on Col. Packanham ..... and Price ....." Expected Thomas Batt to arrive, and on settling the bill, met Batt before leaving on the 16th. Arrived at Smyrna 17th, Syra on 18th where he booked a passage on the "Sinla". Left Syra for Malta and Gibraltar 31st May, arriving Gibraltar 4th June, where he re-joined the "Magician" for the journey along the Portuguese coast, sighting Lands End and the English on 25th June "..... Tuesday, 27th June 2 o'cl. this morning made the South Stack light ..... at 10 made the Copelands and was very glad to see them once more.”
Diary of Robert Thompson March - June 1854. D1559/8 at PRONI. South stack is near the port of Holyhead in Wales and the Copelands are islands at the entrance to Belfast Lough so this was Thompson returning to Ireland.
PRONI also has this:
T956/152 dated 23rd May 1857.
Commrs. for sale of Incumbered Estates in Ireland to Thomas Greg Batt, Stranmillis, Co. Antrim.
Copy conveyance of 33ac. 1r. 16per. I.P.M.
Considn.: £596. 5s. 4d.
The Course, Malone, Co. Antrim.
This is to do with classic sub-prime mortgaging on overvalued property. The Incumbered Estates Commissioners were set up in the 1850s to deal with hundreds, if not thousands, of big Irish estates that were effectively bankrupt. The big estates had frequently mortgaged themselves up to the hilt, and the security for that debt was their income from their tenants. During the 1840s and during the famine in particular many tenants were unable to pay their rent, or at best only a proportion of it. As a result huge arrears built up. The landlords frequently couldn’t service their mortgages and faced bankruptcy. However bankruptcies at that volume would have brought the banks down too, creating a massive national financial crisis. No-one was interested in buying most of these estates because, without the mortgages cleared, they would inherit them. (A mortgage is secured on a property, not a person, so goes with the property if it’s sold and the mortgage not paid off). Not a good buy at all. So the Incumbered Estates Commissioners, later the Encumbered Estates Court, was authorised to auction these properties and get the best price it could, repay what that money allowed, and then the rest of the debt was written off by statute. So making the estates potentially viable again.
It looks to me as though in 1857 Thomas Greg Batt was in deep financial difficulties and had to sell his estates. If it’s the same Thomas Batt as had land in Killygarvan, and Hugh Milligan was employed by him, then this might be behind the decision to emigrate. Perhaps he had lost his job?