And are the suffixes "junior" and "senior" added in the names on passports? And also on identity cards? Or is it just informal and only said aloud?
"Senior", "Junior", and similar identifiers are formal parts of a person's name in any English-speaking country.
Most English-speaking countries don't have identity cards. As for the passport, that would be at the discretion of that country's passport agency, but my guess would be typically yes.