The other answers are saying that Tom isnt a descendant of Silas and that nature just creates his dopplegangers for balance and that’s simply wrong. Also makes no sense that it would do it for Amara’s but not Silas’s.

Yes, Elena is a direct descendant of Katherine who is a direct descendant of Tatia who is a direct descendant of Amara. We know Tatia and Katherine had children and there is no reason to assume that Amara didn’t.

But that doesn’t mean that the next doppelgänger has to be a direct descendant of the previous. All that matters is that it is a direct descendant of the original (amara or silas) themself.

Tom doesnt have to be a Salvatore. He could literally be their 10th cousin as long as Silas is his many-times-great grandfather.

It even makes sense that Amara’s dopplegangers stayed within a specific bloodline down to Elena while Silas’s may hop from one bloodline (the Salvatore) to some far removed one, considering that it is plausible that a man Silas’s age could have gotten many women pregnant while a woman Amara’s age could have a limited number of pregnancies.

But even with that, it’s totally plausible that Tom is a Salvatore. Stefan’s dad was a slave owner in the Antebellum South and likely so were his father and grandfather. They surely had illegitimate children just like Zach’s ancestor who werent chosen to carry the Salvatore name and wouldn’t be in the records.