(Humble) one’s wife; a humble term used by the speaker to refer to his or her own spouse.
私の家内は医者で、病院に勤めています。
My wife is a doctor and works at a hospital.
家内の承諾を得てから決めます。
I'll decide after getting my wife's approval.
彼はいつも『家内は忙しい』と言って外出していた。
He always said 'my wife is busy' when he went out.
The inside of the home or one’s family; refers to household/internal family matters.
家内での決まりごとを全員で確認した。
We reviewed the household rules together.
家内の事情で出張をキャンセルした。
I canceled the business trip due to family matters.
家内安全を願って神社にお参りした。
We visited the shrine to pray for the family's safety.