A woman who repeatedly asks a man she knows to be gay when he's going to get married and have children is not trying to let sleeping dogs lie.
There's simply no way you can tell a woman you work with that you disapprove of her relationship with her adult child, no matter how much you think it would be better for him to move out.
Don't badger people without children into admitting the secret desire for children you're sure they have to you! Don't badger anyone! Leave the badgering to the badgers.
You can't prevent a possible future closeness between your upcoming child and one or more of their grandparents.
A child is not a bargaining chip or a learning tool. Your focus, if you adopt a child of a different race, should be on nurturing and protecting your child from bigotry, not deploying him or her as an anti-racist Mr. Fix-It.
There are alternatives to pregnancy if you want another child.