If you are comfortable creating computer spreadsheets, or even just a word processed document, you can create a table to house your collected information (list all the relatives down one side, the health and medical conditions across the top, and put checkmarks in the ones that intersect).
If that's more than you want to tackle, consider using the Family Health Portrait, from the U.S. Surgeon General and the U.S. Department of Health and Human Services. It helps you track all necessary blood relatives, plus charts people and diseases for you. The information gets saved to your computer.
