The best solution to the problem would be to form an independent city-state [basically relocating the Dalton seat of power] on a river and/or the coast but still closely located to a good supply of materials.
Invite the remnants and the Dalton estate staff/workers/resident [all the people that would be loyal to Maria] and cure them of the fertility problems.
Then invite anyone needed to fill skill gaps, like farmers, carpenters, foresters, sawyers, tailors/leathersmiths, stone masons and blacksmiths, get them situated with their family unit.
The remnant and the trusty-trio would be capable of providing an initial level of security.
After that, every person could be inducted into the city militia and at a minimum trained to use bows and craft their own arrows.
Then once the new settlement is self-sustaining trade can be formally established with the original island and eventually more people from the original island can be cured, with various selection criteria.