My mother and her siblings were basically the same, except their voice qualities were more varied. Two were heroic operatic Tenors, one was an operatic Baritone, one was a lyric operatic Soprano, one was a pop low alto, one was a "red hot mama" pop singer, and the other brother preferred playing an instrument.
My seven children are good singers, too. The girls are all "mugwumps" meaning they can sing any part, though some of them actually have part preferences. The three boys can sing Tenor, Baritone and Bass, though we hardly get a chance to sing together any more. Our families are spread out across America from east coast to west coast.
Providing enough "money notes" for our various singers means that we don't stay in one key very long, usually. Modulations are an absolute necessity! Besides, we each like to get a turn singing the melody. So, arranging, for me and my siblings, is always a labor of love.
Here is an arrangement of "Love at Home" that started with what my mother whipped together for us. She was such an accomplished pianist that she never really wrote the music out. We just had to learn what she decided for us. And she just played what she wanted to play at the time for accompaniment or she had us sing a cappella. Later, after I learned about notating music, I started writing out arrangements. I may or may not have added my own touch here and there.
This arrangement I actually wrote out for us to sing at my mother's funeral. Try counting the "money notes."