Is it permissible to go and meet the suitor with the mother and a friend before the suitor comes to propose to her at her home?

A suitor is considered a stranger (non-mahram), and it is permissible for him to look at his fiancée, whether with her knowledge or without it, due to the permission granted by the Lawgiver for that. If the suitor wishes to see his fiancée outside the home in the presence of her mother and her friend, provided that Islamic guidelines are adhered to—such as proper hijab, avoiding seclusion (khalwa), not speaking in a seductive manner, and being safe from temptation—then there is no harm in that. However, it is preferable that the viewing takes place in the presence of one of the fiancée's mahrams.