Handling questions/observations about donor-conceived baby

My wife and I have two daughters.  The first was born from my egg and a sperm donor.  The second, whom we just welcomed, was carried by me but came from my (trans) wife’s sperm and an egg donor.  So there’s no genetic relationship between me and the new baby, or the two sisters, though of course there is plenty of love!

Some people have made comments about how much the new baby looks like her sister.  Some people have made comments about how different they look.  I’ve been at a loss for how to handle either comment!  I don’t want to go into the nitty-gritty of their genetics with strangers.  But I also don’t want to lie, or make the kids feel like their backgrounds are strange or something to be ashamed of.  Parents of adopted children, stepchildren, or donor-conceived children, how do you handle these comments?