納得 and 一良好な usage in this sentence

Question

What is the meaning of 「納得」 and 「一良好な」 in the following sentence?

仁の家族。仁の人柄がここで育ったのも納得のサムドラ内一良好な家族関係・人柄の一族。旧家で名家。

I think that 「一」 in this case is similar to 「一番」, so I would translate 「一良好な」 as "the best", "the favourite". As for 「納得」, I know it translates as "consent", "agreement", "compliance", but I don't understand its meaning here. The context is a character's family profile in a manga called "Samurai Drive" (「サムライドライブ」, abbreviated to 「サムドラ」here). Here's my attempt:

Jin's family. It's the family in which Jin developed his personality, and also the family with the best relationships and personalities within those agreed(?) in Samurai Drive.

Thanks for your help!

Answer 1

～ + も/は + 納得だ/納得がいく/納得できる means "(therefore) ～ seems reasonable/legitimate/understandable", "so, that explains why ～", etc. ～ is a consequence part, which is often undesirable and/or unlikely.

• 高級な素材を使っているので、値段が高いのは納得がいきます。
• このレストランの料理はとてもおいしい。なかなか予約が取れないのも納得だ。
• ここの家族の人柄は素晴らしいので、仁の人柄がここで育ったのも納得だ。

納得の/納得がいく/納得できる + (noun) is "(noun) that convinces someone of ～", "reasonable (noun)", "satisfactory (noun)":

• 納得の値段 reasonable price
• 納得のいく説明 = 納得がいく説明 satisfactory explanation

Put together:

• なかなか予約が取れないのも納得のレストラン
  the restaurant that it is rightly/understandably hard to make a reservation at
• 仁の人柄がここで育ったのも納得の素晴らしい一族
  the wonderful tribe that convinces me of the fact that Jin's personality was developed here

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(place) + 一【いち】 means "best in (place)", "number one in (place)". Parse the sentence as サムドラ内一 + 良好, not サムドラ内 + 一良好.

• 日本一【にほんいち】高い山 the highest mountain in Japan
• フランス一の葡萄畑 the greatest vineyard in France
• サムドラ(内)一良好な家族関係 the best family relationship in Samurai Drive

内 before 一 is not common.