A stepfamily is a multi-generational group of related adults and kids in which one or more adults chooses the of part-time or full-time role of stepparent for their mate's prior kids. So any single bioparent seriously dating or committed to a new partner forms a stepfamily. This is true whether they live together or not.
Re/married couples who conceive a child together and/or whose prior kids are all grown still form a stepfamily. Couples with adult stepkids usually bypass stressful conflicts over child visitation, financial support, and custody. They do not bypass significant stress from false-self wounds, unawareness, ex-mate relations, incomplete grief, and conflicts over stepfamily identity, loyalty, membership, parenting values, money, names, holidays, family priorities, and traditions. example