What are the limits of dress in front of the in-law (hamu), and does it refer to custom or are there শরعي (Sharia-compliant) regulations?

If the "hamu" (in-law) is the husband's father, then he is a mahram to his son's wife, and it is permissible for her to uncover what is usually apparent, such as the head, forearms, and feet, unless there is suspicion. However, if the "hamu" is any other relative of the husband, such as his brother, uncle, nephew, or cousin, then they are not mahrams to the wife, and she must observe hijab in front of them and not display her inner adornments to them, just as she would with strangers. Any custom that contradicts this is not valid.