Questions & Answers about Vanha kartano ja uusi huvila olisivat minun.
How do we build olisivat from the basic verb olla?
To make the conditional (would be), we take the stem of olla, which is ol-, and add the conditional marker -isi-. Finally, because the subject is plural (a mansion AND a villa), we add the plural personal ending -vat, giving us ol-isi-vat.
Why is the verb plural (olisivat) instead of singular (olisi)?
Even though kartano (mansion) and huvila (villa) are singular words on their own, the word ja (and) connects them into a plural subject. Because there are two things doing the action in total, the verb must agree and take the plural ending -vat.
I thought minun translated to the word my. How does it mean mine here?
Why are the adjectives vanha and uusi in their basic dictionary forms?
Because they describe the subjects of the sentence. The subjects (kartano and huvila) are in the basic nominative case, so the adjectives attached to them must also stay in the basic nominative form to match.