Sean or Jean CONNOR or O'CONNOR ?

Hello,
First, excuse my English.

I'm not familiar at all to search "ancestor" in Ireland and I'm a bit lost because I cannot find what I'm looking for and I will explain;
I'm from Belgium and I recently discovered the mariage civil records with the following details (see also file in attachment, in French):

• Mariage between CONNOR Sean and RONSMANS Rosa
• Mariage place: Eugies (Belgium)
• Mariage date: 22 May 1920
• CONNOR Sean birth date and place: 25 August 1893 in Listowel.
  Son of Patrick and Marie KISSANE (it could be Mary Kissane).

So, here are my questions:

1. I would like to find an image with the birth records of Sean CONNOR. But is it Sean or Jean (French translation of John) or is it CONNOR or O'CONNOR?
2. I would like to find an image with the mariage civil records of John?,Jean?, Sean? CONNOR's parents.
3. I found a record within the Irish Census of 1901, where there is a family with a child called John, the father is Patrick but the mother is Margaret (see 2nd attachment file). Does the firstnames Margareth and Mary (Marie) could refer to the same person?

Thanks in advance for you help and your answers.

 Best regards,

      Alain (from Brussels-Belgium)