so stan totally had a secret twin brother right. im not the first one to say this but,

rounder, thinner rimmed glasses.

when he found them in the hidden room he tucked them away before anyone could see

then was just looking at them later

and who is that kid reading in the back, with similar hair

im actually betting that his twin’s name was stanley. in dreamscapers when bill was remembering “stan pines” he was actually remembering stanley, which is why he didn’t say “stanford”. speaking of bill, if you look on his wheel you see both the symbol on stan’s hat and the glasses, meaning they’re 2 separate people.

perhaps stanford and stanley were searching for the secrets of gravity falls together, that’s why grunkle stan was so adamant about lying to the kids about the stuff going on to keep them safe, he knows how dangerous it is because he lost his brother to it?

also:

the “stanley mobile”. did stanford take stanley’s car after something happened to him?

and since stan and the kids share the same last name, stan must have had a brother, and that brother must have had a son, and that son is dipper and mabels dad. so “stanley” would be their grandfather. that would have made whatever happened to him hurt more for stanford, he already had a family by the time he disappeared.