Learn Finnish: Olohuoneemme on iso ja tilava. - Our living room is big and spacious.

The word for 'our' is built directly into the noun using the possessive suffix -mme. Olohuone means 'living room,' so olohuoneemme means 'our living room.' You could also include the pronoun meidän (our) before it, but the suffix alone is perfectly fine and very common.

Does adding the suffix -mme change the stem of the word olohuone?

Not in this case. Olohuone is in the basic dictionary form (nominative). To add a possessive suffix to a basic-form word that already ends in a vowel, you usually just attach it directly to the end. Since olohuone ends in e, the -mme attaches without any changes to the word itself.

How would I change this sentence to say 'your (plural) living room'?

You would swap the first-person plural suffix -mme for the second-person plural suffix -nne. The word becomes olohuoneenne, making the sentence Olohuoneenne on iso ja tilava.

Are iso and tilava both adjectives, and do they need to match the noun?

Yes, they are both adjectives: iso means 'big' and tilava means 'spacious' or 'roomy.' Because the subject olohuoneemme is singular and in its basic form, the adjectives also stay in their basic singular form.