Why doesn't the father reveal the letters?
In Invisible Life (2019), after they find out "Guida is dead", the father says he's sorry and feels shame for not telling the truth about Guida having came back. Then, from this point onwards, the father should not be mad at Guida anymore.
Those letters being Guida's most important legacy of Guida, why didn't he reveal the letters from Guida to find out what happened, either by reading the letters himself or giving them to Eurídice, after the "Guida is dead" thing? Even if reading those letters brings more pain, at the same time it brings answers which is a much more positive thing than the pain.
There is no secret to keep at that time, all secrets have been revealed, except for possible facts in the letters which can't be known unless someone read them.
Even if he really want to keep one or more secrets, he should first find them out the secrets by reading the letters then throwing them away, not keep them in a box that family members can open in the future. If he did so, he would find out Guida is alive and every one would be happy.
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