FamilyInstance instance;  
var typeid = instance.GetTypeId();  
var symbol = RevitDoc.GetElement(typeid) as FamilySymbol;  
var familyName = symbol.FamilyName; 


var defaultFamilySymbolID = family.GetFamilySymbolIds().ToList()[familySymbolIndex];
var symbol =  doc.GetElement(defaultFamilySymbolID) as FamilySymbol;
if (!symbol.IsActive)
{
    symbol.Activate();
}