Some women are lenient about shaking hands with and kissing men.

Men who are not mahram, like relatives such as the son of a maternal uncle or aunt, claiming that they grew up together or that he is younger in age.

And that this is permissible—not permissible, of course, not permissible. The Prophet ﷺ said: The brother-in-law is death, meaning the husband's brother.

She grew up with him, especially if she—

For example, her husband's older brother got married, and she has been married for a long time, and he was a child, six years old, when she married, for example.

When they grew up, she is like his mother.

But it is not permissible for him to kiss her, nor to kiss her as if she were a stranger.

Do not say, "By Allah, he is like my son." No, being like your son is one thing, and your son is something else.

So it is not allowed, of course, and such matters must be rejected.