By Determiners, Singular verbs

It's the same in BrE; either a singular or a plural verb can be used after 'family'. My family was/were in Orchard Road last Sunday.

You need some sort of determiner before "meal." In the U.S., we generlaly use a singular verb for family, but would still use "their" in the plural. The dining area is where the family has/eats their meals.

The determiner 'every' is always used with a singular noun and a singular verb. The other determiner 'all' can be used with singular/plural noun and singular/plural verb.

'Group' is a singular noun (and 'each' is a singular determiner)-- so a singular verb is required: 'each group is/has...' And of course the full sentence should be: 'Each group has its own merits'.