[annalex]

Of course if one has chosen “brothers” to signify a group of cousins, second cousins, and sundry relatives, then in a possessive case we get “his brothers”.

[Uncle Chip]

Of course if one has chosen “brothers” to signify a group of cousins

And just why would one use the word "brothers" to signify "cousins" when the language already has a perfectly good word [suggenes] meaning "cousins" to signify "cousins"???