"older siblings" and "younger siblings" should be accepted too
if there is no determiner (e.g. seorang), do we know that he has just one oler siblign and one younger sibling? Could this sentence also mean "My husband has older siblings and younger siblings"?
yes it could mean that, if you want to specify it you just have to specify it on how many siblings one has.
Very unnatural way of speaking. Moreover it is known that my husband has an older sister and a younger brother or sister.
I am not sure why you think that the solution is unnatural. I can easily think of one context where it would fit properly. It is nice when sentences build up on previous ones but they don't have to...
Sorry, I was thinking of the Malay version of kakak which is meant for older sister only.
kakak-kakak = more older siblings? lol
kenapa pakai "an/a"? kan tidak dikatakan ada "seorang"