I agree with most of the points that Mr. Kennedy stated in his answer to you.
He is absolutely correct that the results will depend on what the Will says about alternate beneficiaries. However, California has what is called an "anti-lapse" statute that states if a beneficiary "fails to survive" the person making the gift, the "issue" of the deceased beneficiary receive the gift in place of the deceased beneficiary unless the Will expresses a contrary intention or makes an alternate disposition.[Cal. Probate Code Sec. 21110]. It goes on to state that if the Will requires the beneficiary to survive the person making the gift, that will be considered a "contrary intention".
So, for example, if my Will says "I give my house to my son if he survives me" and my son does not survive me, then the house passes pursuant to other provisions of the Will.
Assuming a competent estate planning lawyer drafted the Wills, it probably provides something like "if my son doesn't survive me, then this gift shall be distributed to my son's issue by representation (or by right of representation)." In that case, the Will, in effect, provides that the gift is distributed to the son's children (you and your siblings, if any) who are alive at your grandparents' deaths and to the children of any deceased children.
It is unusual (but certainly not impossible) for a Will to provide that the gift would go to the son's wife if the son were deceased. But I have clients who have done that, so I won't categorically state that "it would never happen".
Two other things to mention ... first, if your grandparents sell the house before their deaths, then the gift "lapses". Second, if you do inherit the house from them make sure you check with a competent estate planning lawyer ASAP - you might be able to keep your grandparents' property tax rate under California "Proposition 58" [the little-known "grandparent-grandchild property tax reassessment exclusion].