You can't equate sin and "against the teaching of the Church". Sin is an action, Church teaching is an abstract truth. You can't just put one on each side of an equation. You can sin and still live in accordance with the teachings of the Church, this is what the Sacrament of Reconciliation is for, because we can't help sinning. But Reconciliation does require us to turn away from our sins.

Homosexuality is not the disqualifier here, but persistence in sin in defiance of the teachings of the Church.

And I believe the same metric can and should be applied to children whose parents are known to not married, or to have divorced and remarried after an otherwise sacramentally valid marriage, or who conceive their children through immoral fertility treatments, all of which disdain the teachings of the Church on the sacrament. However these things are not plainly observable in the fashion that a same sex couple parenting a child is. While they may violate the teachings of the Church, they may also be hidden from casual observation.