The nuclear family is a historical aberration and it's not unusual for infants to have multiple primary caregivers that they can rely on to get their needs reliably met.

Attachment theory as popularly understood is basically astrology for how you and your mommy got along before you were 18 months old. Attachment is at minimum a dyadic process; an attachment "style" is something that emerges from the social interaction of two or more people.

I could go on at length here.