Bonjour! Le génitif, c'est pas si compliqué, ne t'inquiète pas. Avec un peu d'entraînement, ça en devient très facile. En attendant, voici les réponses de tes exercices :

1) a) Most of Ireland's sheep have a black head.

b) During the conference, the President's action was praised.

c) This Book of Kells was Frank and Margaret's copy.

d) Jeanne Rynhart's sculpture was inaugurated in 1992.

2) a) The Dublin Museum presents their most beautiful treasures.

b) Its success was fantastic.

c) Its independence began in 1922.