[Nagoyankee]

Writing sample:

突然の訃報にただ驚いております。どうかご遺族の皆様 もお気持ちを強く持って、お力をお落としになりません よう、ご自愛下さいませ。心より御冥福をお祈りいたし ます。

Speaking sample:

この度のお父様のご逝去、お悔やみ申し上げます。どう かお気持ちを強く持たれますようお祈り申し上げます。

Remember these are only samples. Only you can expand and make them better because we don't know how close you were to this gentleman who passed or how close you are to his son. I don't even know if you actually should be sounding like a native Japanese speaker in this letter or speech. You won't sound real if you know what I mean.