To be honest, having royal ancestors from 700 years ago is pretty common; our family trees all have around thirty million branches by that point and even though the same people will show up on different branches as families marry into each other multiple times, the odds are still very high for all of us that nobles and royals are hiding somewhere in those leaves. And Robert the Bruce certainly has plenty of descendants; he married twice and had five children plus another six acknowledged illegitimate children... so it's very likely that a sizable percentage of people today with Scottish ancestry are descended from him! But not everyone can document their exact line of descent.
In fact, Robert the Bruce is a Vance ancestor multiple times, because his descendants included the Kennedy family who were aligned with the early Vans of Barnbarroch and intermarried with them several times. The first three connections are shown in the picture below, but there are probably also many later connections from other Vans family spouses who were also descendants of Robert the Bruce through other lines.
Jumping ahead to the 21st century, the Vances of DNA Group 1 probably have the best claim to this ancestry, since their group includes the current Laird of Barnbarroch. But who knows? None of us Vances today (to my knowledge) can reliably document our exact tree back this far, so it's a possibility still for most of us. For now, the best we can say is that if you have reason to believe that your family tree goes back to any of the Vans family of Barnbarroch, then you also have reason to believe that King Robert the Bruce is your ancestor through the family connections shown here.