This is strange question but my dear mother has been wondering about the funniest things ... she is to hold my grand fathers (her father) wake at her home and she wonders if it is ok to leave out the with sympathy cards?
I'm not sure there is a fixed right and wrong in this. You could either have them out, to show how many people thought highly of him - but this might not work so well given that many people prefer to write letters, which don't lend themselves to display. Or you could have none, because you prefer to keep them private.
I think that the principal mourners should decide for themselves what they want to do, and then do it. No need at all to justify the decision.