He accepted his stepson's decision without recrimination.

Grumbler, thank you!

He was a really good sport about his stepson's decision./He took his stepson’s decision like a champ/with grace. (?)

Ого, Татьяна жжет!

Thank you, Tatiana, for sharing your knowledge.

Tatiana's variants would be valid if the decision personally impacted the speaker. For instance, if the speaker needed a kidney transplant and the stepson was the only candidate but refused to donate his kidney. I don't think the Russian version affects the speaker in that way — the stepson's decision is simply not the speaker's cup of tea but he doesn't judge or reproach him for it. Am I right?

Absolutely🙏

Uly, thank a million!)

👍🏻🤩