I'm not aware that family structure is really part of Marxist dogma at all.Marxists are usually interested in keeping family structures
Marxists have criticised the "nuclear family" construct on a number of bases, none of which are fundamentally opposed to the idea of two parents bringing up their biological children. The major issue is more that the family unit can be used to convey forms of privilege (e.g. inheritance of wealth), and that it has been manipulated by capitalism via notions of competition and consumption beneficial to the capitalist class rather than themselves.