How can I combine kids' first names with Power Query if they have the same parents?

1. If there is only one child, then we lease it as it is.

2. There are two kids, and their first names are A and B, respectively, then we combine their first names as A & B.

3. There are three kids, and their first names are A, B, and C, respectively, then we combine their first names as A & B & C.

Only up to three kids, the most.

Thanks!

Jim