How do I legally exclude my sons-in-law from receiving any proceeds from my estate?

You write a will, and in the will you name the specific people who will inherit from you--and those people will only be your blood relatives. The limitation is, you can't control what your blood relatives do with the money after they inherit, so a daughter could share it with her husband, her ex, her new boyfriend or fiance, etc. Therefore, you way wish to instead of leaving it to your daughters, in your will create a "testamentary trust"--one that only comes into being after you pass--which will use your estate for the medical care, basic support (if necessary), and education of your grandchildren, with the trustee(s) being someone other than your daughters (who may be persuaded to try to use the money for their husbands) whom you trust, like a sibling, trusted lawyer or accountant, good friend, etc. That way, the money can *only* be used to benefit your grandchildren; of course, some indirect benefit will flow to your daughters and their husbands (e.g. they won't have to save as much for college, giving them more discretionary income), but this will maximize the chance of only blood relations (the grandchildren) directly benefiting. Any lawyer who does wills can draft a will, including using one to set up a testamentary trust, so you are advised to consult with an attorney.