- Tua is only "your" (for singular person, for plural person it's "vosso/a").
- Sua is originally meant to be 3rd person. (His/her/their), but can be used for 2nd person too.
That's because "você" is a treatment pronoun. It refers to the second person, but all conjugations for it follow a 3rd person pattern. Compare this to English in "his/her Majesty wants....". You are talking to a 2nd person using 3rd person conjugations because of the treatment. Of course "você" is not formal.