My wife wants me to marry her brother’s wife

I don’t know what to make of this or if I should even go along with it.

My brother-in-law, my wife’s only brother died about a year ago leaving his young wife and two kids.

Their parents had only the two of them and all they had was each other after the death of their parents years ago before I even married her.

We have two kids of our own.

Her brother’s wife informed my wife that she might soon be open to remarry and have a man in her life as she is still very young.

My wife has been troubled since then as she is concerned about the well-being of her brother’s children who she claims can never be well taken care of in another man’s house.

Yesterday she told me that she had discussed with her brother’s wife and they agreed that I would marry her brother’s widow.

She claims that with them in the family, she can take better care of them while I give her brother’s wife the cravings she might desire from a man.

The lady in question is very attractive but will this not lead to trouble in the future? Please advise me on what to do. I’ve not heard this happening anywhere before.