[Grammar] his family is/are having their dinner

[Oceanlike]

I have chosen a plural verb for the question below due to the presence of 'their'. In the absence of 'their', I would have chosen 'is'. Is my way of thinking incorrect since 'His family' is clearly singular.

His family are having their dinner tonight at the Coast Garden.

Thank you!:-D

 

[Tarheel]

"His family are having dinner" would, I think, be correct in British English.