In the first sentence, it sounds more natural to use the past simple for all the verbs. These are three similar actions which happened in sequence on the same occasion, so it isn't necessary to use a past perfect for the first one. It's fine to say "After he arrived home, he unpacked and went to bed early." You could use a past perfect, but it would sound less natural. In the second sentence, you might use a past perfect. This is because we have two very distinct and different time references in the past: the point at which they got married and the period leading up to that point. You could say " My grandparents had only known each other for a few months before they got married." (But note the word order: 'only' has to go before the past participle). But you could equally well say "My parents only knew each other for a few months before they got married": this wouldn't be wrong. Many students and teachers cling to the mistaken belief that if you have two things happening in a past narrative, the one which happens first has to be in the past perfect. This is not true at all.