Sorry to be stupid, but how does biro relate to family?
I believe it's being used to reinforce the concept of possessive pronouns (his/her/your).
Honestly I have never heard the word biro in English, I had to Google to find out that it's one of the rarer words for ball pen. Is it necessary to use this word here?
Yes, because it's what the Welsh use for pen. I asked my tutor what the word pen was before the biro was invented. She thought perhaps ink pen!
How does his biro translate to "ei bin" as biro is a tradename?