"They are full."

Translation: Sunt plini.

[Tony602713]

One, Sunt plini, two, Ei sunt plini, maybe i dont understand

[-Afina-]

The "they" in the questions asks for plural, therefor it's "Ei sunt plini" but you can leave the "ei" because "plini" indicates that it is plural.
Singular, i.e. "I am full" would be "(Eu) sunt plin", again "plin" indicates the singular in this case and "It is full" would be "Este plin" if I'm not mistaken.

[mihaigrigo781942]

Full=plini,satui,

[YuukiMory]

What the hell? Even if i can not use Ele or Ei why it's mistake then i use it?

[Ces.10]

What did you use? If you used 'ei sunt plini', no problem :) But for 'ele' that wouldn't work you'd need to use the female plural: pline