は父親の

his father's

→ は
phrase Common #6,334
his father's は marks the topic, while 父親の means “father's.” This phrase usually comes before a noun, such as 父親の会社 (his father's company).
JA: 彼は父親の店を手伝っている。
EN: He helps at his father's shop.

トムは父親の財産を相続した

Tom inherited all of his father’s assets.

ポールは父親の代わりにパーティーに行った

Paul went to the party in place of his father.

ベンは父親のこと知らないわ

Ben knows nothing about his father!

— ダーク・プレイス (2015)

ケンは父親の誕生日に上等なワインを買った

Ken bought a fine bottle of wine for his father’s birthday.

トムは父親の事業を継ぐためボストンに戻った

Tom returned to Boston to take over his father's business.

そのマリファナは父親のだよ

That marijuana belongs to my father.

— ダーク・プレイス (2015)

トムは父親の話に全く耳を貸そうとしない

Tom refuses to listen to anything his father says.

スーザンは父親の靴を磨いた

Susan polished her father's shoes.