What if I’m still legally married to my spouse but we have chosen to separate rather than divorce and I execute a Last Will and Testament wherein I leave all of my property to my son or daughter?

Spouses have certain legal rights to your property that cannot be assigned away in your Last Will and Testament regardless if you are separated from that spouse or estranged from that spouse.  The length of separation or estrangement does not matter and your spouse would still be entitled to his/her statutory legal rights to your property.