Full grown kissing gouramies, most in a 30g tank, 0. One, a 12" full bodied fish belongs in a tank at minimum 55 to 75 gallons. Two adult kissing gouramies are not peaceful fish, unless you have a really large tank, a pair is the most you should have. Three, they need hiding spots, meaning rockwork, which will take away from the volume of the tank.
They should take about 2 years to reach ~10, then they grow slower to ~12" max. The "kissing" is most often seen when they are trying to eat foods of the rocks or the bottom of the tank, or in a tank that does not allow enough room for more than two, it is a sign of aggression.
Anyways, kissing gouramies do not belong in a 30 gallon tank.