Were the twins killed because Mrs Johnstone told them they were twins or because of something else?

The twins could have been killed for a number of reasons, which one do you think it was?

1.The superstition-At the start of the play Mrs Johnstone gives Edward away to Mrs Lyons, but she makes Mrs Johnstone swear to the bible and tells her that 'If the Mickey and Edward find out that they are twins they will both be killed.

2.Linda-Linda makes two mistakes in the play the first being that she kisses Edward when she is married to Mickey making him angry, and the second is forcing Mickey to stop taking the pills, this makes him, uncontrollable in the end.

3.Sammy-Sammy kills a man with a gun and then runs away with Mickey before they get caught. Mickey sees where Sammy puts the gun, which he later uses to kill Edward.

Comment which one you think it was.