Without being specific, cracks in the walls of old houses, even if qhite large, are not normaly a problem unless it is either new, or involves a unsuported corner.
Our house had one large crck going from the front door lintel (crackedas well) right through 2 storeys to the roof eaves, at which point you could put you arm through.
No problem said our builder friend, we'll just dig out a slit in the wall at the bottom and cast a concrete load bearing lintel then you can just fill it in.
If it has a number of cracks it might be more of a problem.
I dont know of any surveyors on the island I suppose you would need to consult an architect or like us the local builder.
Remember if you are proposing to replace the roof at some stage you are required to form a wring beam round the top of the walls, so this would lock all the cracks in place, and prevent them from increasing.