An heir is one "who is entitled under the statutes of intestate succession to the property of a decedent." UPC § 1-201(20).
No living person has heirs, only heirs apparent. Heirs apparent have a mere expectancy that is both contingent on their surviving longer and on the property not being otherwise disposed of.
When named in a will, heirs apparent are called devisees, legatees, or beneficiaries. This is still contingent upon the same conditions however and does not guarantee that they will inherit anything though until the testator actually dies.
Expectancies are not legal interests and cannot be legally transferred, however purported transfers may be enforced for equity's sake.
Rules for Heirs
In every state, the spouse is first, then descendants take to the exclusion of ancestors and collateral kindred. (Dead childrens' wills do not apply. In-laws get nothing.)
No Descendants or Parents
In the UPC, the spouse gets everything. UPC § 2-102(1)(A).
A parentelic system looks up generations of ancestors until there is a living descendant in that parentela, or line. (i.e., look at the grandparents, then the great-grandparents, etc. until you find someone with a living descendant, then split all the amount among his descendants only.)
E.g, a first cousin would be chosen over a great-grandparent because a first cousin is a descendant of a grandparent, which is a closer parentela.
Under the Modern Per Stirpes system, shares are divided equally to children, but if all children are dead, the property is divided among grandchildren. Thus, all grandchildren get the same amount if all the children are dead. If some children survive, it is the same as English Per Stirpes.
Modern Per Stirpes applies the same with grandchildren and great-grandchildren. The division does not occur until the first generation with a live taker.
Modern Per Stirpes has horizontal equality—children/grandchildren get equal amounts—whenever all children are dead.
Under the Per Capita at Each Generation system, shares are divided equally to the first living descendant generation (where it is divided equally among the living children and children with living descendants), then if one or more are dead, the reminder is divided again to their children. Thus, all "grandchildren" always get the same amount.
A negative will is where one specifically says that someone does not get something. This enables easy disinheritance.
Historically, negative wills were not allowed. To disinherit someone, it was necessary to specifically give away all of your property to others. Anything not given away in a will was able to be contested by the attempted-disinheritee. Now however, both the UPC and Virginia allow negative wills.
Adopted children are the children of the person/people who adopted them, not their biological parents. (Unless adopted by the spouse of a biological parent—that doesn't stop a child from inheriting from his biological parent too. UPC § 2-119(b)(2).) UPC § 2-118, UPC § 2-119, VA Code § 64.2-102.
However, this does not allow inheritance to pass back up from the child to the father and his family unless the father has openly treated the child as his and has not refused to support the child.VA Code § 64.2-102(3)(b).
A posthumously conceived child is one conceived through artificial insemination after his father's death by means of sperm he had frozen during his life.
Under UPC § 2-705, posthumously conceived children can inherit if the distribution date is the date of the parent's death, the child was conceived with 36 months or born with 45 months of the death, and the decedent consented to posthumous conception, proven by a signed writing or other clear and convincing evidence. (This still requires state law to permit it however.)
A surrogate mother is one who agrees to carry and birth a baby for others. The baby may or may not be genetically related to the surrogate.
UPC § 2-121 provides that surrogates do not have a parent-child relationship with their child unless no one else does. The intended parents do if they functioned as parents within two years of the child's birth.