Agrarian also touched on another part of Slava which I neglected. Cities, organizations and so on in Serbia have a patron saint -- and therefore their own Slava. Many people in Serbia refer to significant dates by Church calendar name rathere than the Roman date -- such as "the Agreement on the day of Assumption" or "the St. Vitus' Constitution," etc.
I had never noticed that koliva for a Slava celebration didn't have a candle, but the explanation on your web-page does a good job of explaining the reason.
It confirmed what I had always understood, namely that the koliva at the Slava is primarily for the departed of the family. (And of course just in any memorial service, the koliva is first and foremost an expression of faith and hope in the coming resurrection to eternal life of those for whom we pray.)
In the different tradition churches I have been to, there has never been any universal custom regarding whether a candle is in the koliva or not.
Don't feel bad about the kolach not turning out right. My wife is an expert baker, and making kolach turn out right is very difficult. She spent a day a couple of months ago with an elderly Serbian lady at our parish, helping her prepare kolach for the lady's family Slava, picking up tips...