Much of what he’s referencing in this is pulled from the OT.
Multiple wives were allowed, but never encouraged; and generally wound up ending poorly from all involved.
As for the Siring a child with your brother’s widow thing, that was a cultural law, and one which is not longer enforced thanks to the New Covenant of Jesus Christ.
There are lots of things like this in the OT, and what’s important to remember when looking at them is that those laws were mostly developed to guide a tribal society, distinctly different from what we have today. It is necessary to look at the context of the laws within that society, as well as to look at if those laws are dealing with societal issues or moral issues. For instance, the law about not mixing fabrics in your clothes was a societal law, meant to separate the Jewish people from non-Jewish tribes, not as big an issue nowadays; however, the laws dealing with, say, murder or homosexuality were moral in nature, and therefore remain important to us.