上面已經有人講只要話係同居已經搞掂
仲要咩同居證明都唔駛拎出嚟

英國政府方面係咁樣講
Your family members
If you’re a British national (overseas), your family members can apply as your ‘dependant’ if they normally live with you.
A dependant can include your:
husband, wife, civil partner or
unmarried partner
child or grandchild under 18
child 18 or older, born on or after 1 July 1997 (and their partner or child under 18)
parent, grandparent, brother, sister, son or daughter (18 or older) if they live with you and are very dependent on you for their care
When you apply, you and your family member will need to provide evidence of your relationship and that you normally live together.
https://www.gov.uk/british-national-overseas-bno-visa/your-family-members
至於父母果個就係證明到係very dependent on 果個人就得
但係就冇講過果個人係咪一定都要係BNO holder
我係聽講只要果個人有BNO visa而佢父母又非常依賴佢就可以申請埋一份
亦都聽講有類似既case
當然呢個要再fc
不過如果係真既話就真係表示好多人都可以一拖幾其至十幾
