Dear Abigail,

My sister has chosen to have a baby on her own using a sperm donor. I am excited to have a niece or nephew, and for my children to have a cousin.

My parents, who are in their late 70s, are stepping in to help co-parent with my sister. While she has a very good job, she is moving in with my parents indefinitely. She says she needs my parents’ support because she has to maintain her social life. She can’t take a baby on a date, she told me.

My parents have not babysat for my kids since my youngest was born, almost three years ago. I live an hour from them. When I asked them to watch my kids last year so my husband and I could celebrate our anniversary, they said no. They were just too busy.

My parents paid for my sister’s fertility treatments. To make it fair, they gave me the same amount of money. This was appreciated, since paying for day care eats up most of my salary. But why do I receive help only when my sister needs something?

I don’t understand why my sister would want to move back in with my parents, or why my parents are encouraging her to do so. I don’t understand why my parents would help raise my sister’s child when they are not willing to even babysit mine.

How do I get past this? My sister and I have always been very different people. I don’t want the same things she wants, so why does it matter what my parents are giving her? I have a great life. I don’t want to be angry. I don’t want to feel like a stranger in my own family.

—Megan, 41

Megan,

Which one of your kids is your favorite?

Think hard and tell the truth. Which one do you love the most?

You know, as well as I do, that these are absurd, unanswerable questions. You have the kid who shares your sense of humor, the one you can tease. The one who is easily affectionate and the one who’s full of earnest complaints. The one who is proudly self-sufficient and the one who comes to you with puppy eyes. The one you worry about and the one who puts you at ease. And the descriptions shift their referents on a merry-go-round and none of it corresponds to the measure of your love...