My biggest concern is that the author will turn them romantic from editorial pressure (saw that happen before with hidamari ga kikoeru). If they really want to label it, as this chapter seems to be pointing to, partner is good, isn't it? A life partner.
I want to avoid the "family" title as well, I'm STILL really happy that their priority relationship is not sexual, romantic NOR familial. It warms my heart to see that this option of life style is on the table.
Maybe it's because I'm aro and I'm used to seeing partnering aros talking about their qpr/qpp, but it does feel like a food enough word for me.