my dad has a low sperm count, and him and my mum tried for 5 years to conceive me and my sister.
they ended up having to get a sperm doner,
so techniqually my biological father is a sperm doner

but if this is the road you have to take (which i hope it isnt)..the doctors suggest you tell your kids that there dad isnt there biological one..but my advice, being one of those kids is that i'd rather not no.
good luck ttc..best wishes xx