"You are similar to your dad."
Translation:Jesteście podobni do swojego taty.
You mixed singular "jesteś" with not masculine-personal plural "podobne".
"podobne" is also neuter singular, true, but I don't think anyone would say that, even to a child ("dziecko" is neuter), gender would really rather be specified here.
How many "fathers" one could have? Therefore aswer "Jesteś podobny do ojca" should be correct?
Yeah, I guess just "do ojca" is okay enough to be accepted, although in this sentence I'd use "swojego".
"swojego" is a lot better than "twojego" whenever it's used.
Well, I could add "twego", but I think I could count reports of such pronouns on one hand's fingers. "twego" is kind of a poetic version, not used that much normally unless you like playing with language.
Added here, because why not, but I'd discourage you from trying to use it in your answers because for 99% it won't be accepted. But it's good that you know of its existence.