'The length of mourning depended on your relationship to the deceased. The different periods of mourning dictated by society were expected to reflect your natural period of grief. Widows were expected to wear full mourning for two years. Everyone else presumably suffered less – for children mourning parents or vice versa the period of time was one year, for grandparents and siblings six months, for aunts and uncles two months, for great uncles and aunts six weeks, for first cousins four weeks.'
For women - in-laws were socially considered your family and should be mourned for the same length as natal family, so your mother in law should be mourned for the same length as your mother, and so on - or really as long as your husband was in full mourning.
For men - they could be treated the same as more distant relatives.
There were depths of mourning as well, but that was mostly just for widows - so fully black for a year and then just dark colours accented by black for another year.
For little girls (under 6) their mourning colour was actually white but with a black ribbon broach type thing
We have a picture of my great great grandmother with her 3 favourite children in mourning wear, she had 8 living children total at the time- so sick burn on the others.
Lady is a star