Twin studies are explicitly about scrolling for this kind of family bias.
https://www.psychologytoday.com/gb/blog/looking-in-the-cultu...
"Although many twin studies have been conducted (which is quite an understatement; there are almost 9,000 hits for “twin study” on PubMed!), there have long been critics who argue that they are scientifically worthless."
Smith, Jinkinson. (2020). The debate over twin studies: an overview. http://dx.doi.org/10.22541/au.159674847.78026661
"Because heritability is defined by both genetic and environmental influences, it is not a fixed characteristic of a disease or trait, but a population-specific estimate, analogous to, for example, the mean height, cholesterol level or life expectancy in a population. It also cannot be interpretated at the family or individual level."
Kaprio J. (2012). Twins and the mystery of missing heritability: the contribution of gene-environment interactions. Journal of internal medicine, 272(5), 440–448. https://doi.org/10.1111/j.1365-2796.2012.02587.x