Tommy and Siddhartha - you are both right, but all that doesn't change the fact that in the book the Sittaford Mystery, in the second chapter Ronnie is the one who suggests table-turning, and in chapter 30, Emily (who has solved the mystery) says Barnaby deliberately engineered it.In this case I think it is a simple mistake by AC. Interestingly enough, in the "retrospective" books - Elephants can remember and Five little pigs - she deliberately has people tell about the same person or event in different variations, not just because one of them (the villian) or more (people who want to protect the innocent) are lying, but because memories have faded and become distorted. One of Poirot's tasks is to weed out the misconceptions and false memories and arrive at the truth.
Again, I agree with you Tommy - it could have happened that way - but there is no indication of that in the book. From my perspective, that is either a mistake or cheating on the part of the writer (I'd go for mistake - it happens).
As far as I know, A catholic can get a divorce and remarry by the civil authorities. However, his/her divorce and remarriage will not be acknowledged by the catholic church, and he/she will not be allowed to take part in certain catholic religious rituals (e.g. communion).