What about words like llamáis?

Hola Sanjana

The word "llamáis" has two syllables: lla - máis 

The second syllable has a dyphtong formed by a+i (belonging to the same syllable) 

As it ends in -s and the stress is on the last syllable, you need the accent. The present conjugations of vosotros often end in -ais / -eis and they are all accentuated, unless the word is monosyllabic (vais, veis, dais...):

tenéis, ponéis, queréis, habláis, llamáis... 

This is a very comprehensive article about accents and includes diphthongs and triphthongs. Have a look here.

Saludos

Hola R H.

There´s an accent on veintiséis because there are 3 syllables: vein-ti-séis - the last syllable takes the stress on the é and as per accentuation rules it needs a written accent because the word ends in -s.

Seis is a monosyllabic word because the vowels e (strong) and i (weak) form a diphthong. Here's a lesson on accents when there are diphthongs. (seis doesn't have a written accent because it is only one syllable)

Let us know if you have more doubts after seeing the lessons.

Un saludo cordial.

Inma

Hola Inb

If you saw this written as "llamais" then the stress would be in the first "a", first syllable. This happens with other conjugations in the vosotros form in the past tense (imperfect), for example:

"trabajabais" has the stress on the penultimate syllable, and it also ends in -ais, like llamáis.

There is no written accent in trabajabais.

Saludos

Hola Inb

- áis is pronounced as one only syllable: [ais] (e.g. bailáis, cenáis, trabajáis)

- aís would be pronounced as two separate syllables: [a] [ís]  (e.g. yo aíslo, tú aíslas...= present conjugation of verb aislar = to isolate)

- ais would be pronouned as one only syllable: [ais]  (e.g. paisaje, paisano)

Saludos