What is it called when you fill in the lives of the patriarchs or any biblical person with day to day meaning based on what you would imagine their lives to be like given the information known from the text. Example, we do not know how Jacob dressed, but based on information from other text, we might assume he wore a robe, a turban, had a beard, dressed in finery, carried himself in a certain way, etc. we might also make up stories about his interactions with his many wives based on similar circumstance even from modern writings. These could be true or not, but in any case, add meat to the bones of lives of these otherwise extraordinary people. So, what is it called? Would that be something akin to a drasha?

If you are "filling in" or embellishing details to make it more interesting as you tell the stories to your children, that's ok, especially if you have historically researched that period. But in general, we can't compare ourselves with our ancient rabbis who wrote the midrashim about 1,800 years ago, for they were significantly closer to the giving of the Torah, and had traditions which they gave over through midrashim, which are not made up, but actually happened. Also, sometimes they teach us additional significant messages through these seemingly 'side issues". In order to understand which midrashim are meant to be taken literally and which not, see: https://www.yeshiva.co/ask/57509