"Her siblings and his siblings."
Translation:A siblíní agus a shiblíní.
OK, I'm not understanding this either. I have read a couple of times now about Duolingo instructions of some sort - is there an actual course or instruction? Cause I've gone into this cold and am just kind of guessing as maybe learning as I go along - where can I access the course!?
But this is the opposite to what I have learnt previously ie. a for female (her) adds an h and no h for male . Below it states "a meaning "his" lenites words that start with a consonant" So in this case you have a noun starting with a consonant therefore there should be an h added to form shibliní ?
I can't speak for what you learned, but what you were taught on Duolingo is that a meaning "his" causes lenition: a shiblíní - "his siblings".
Lenition is a process that only applies to consonants. For words that start with a vowel, a meaning "her" causes a h-prefix: a húll - "her apple". A h-prefix is not n example of lenition.