I think if it doesn't matter to you, it won't matter to your babies. I only had one by donor but I have a total of three now. The older two were adopted at birth (no relation to each other) and then lost their adopted parents to death and disability. As far as Shiloh is concerned, these are her sister and brother. She has little memory of life before them (she was 4 when they joined our family).
My 12 year old interacts with Shiloh as though she's been his sister forever. They play or fight like any other biological sibling pair. My 15 year old is a little different. She loves and adores her sister Shiloh. But Shiloh is an added sibling. She was 3 when her brother was adopted and it's obvious to me that the sibling connection is stronger with him. It's not a matter of loving or liking him more. It's just a stronger more solid bond.
In my opinion, if you use different donors but raise your kids as a set of two siblings, they'll bond as such. If you identify and treat them as half-siblings, they will define themselves that way too. I think once you decide what's best for you, that will be best across the board
On a funny note, Shiloh thinks she came to me from God and her brother and sister came from Grandma's house. There's no religion in this ... her name means "God's gift" and she thinks that's literal. At some point she'll learn more but in our day-to-day life, genetics don't matter much!