They can kiss, just as anyone else can but whether you're talking of a kiss on the cheek or a kiss kiss is a different matter. Technically speaking, of course they can, but it's considered incest if it's a kiss kiss which is illegal in some places. They can still do it though.
Brothers and Sisters - 2006 A Righteous Kiss 5-4 is rated/received certificates of: Netherlands:6
He had 11 brothers and sisters.
There are 4 brothers and 3 sister's all up. Assume your one of the brothers - hence you have 3 brothers and 3 sisters. However any one of your sisters, would have 4 brothers and 2 sisters.
he had 2 brothers and 3 sisters
She had 12 brothers and sisters
no she has no brothers or sisters.
yes, 7 brothers and sisters
not have any sisters or brothers
2 brothers and sisters
he had no brothers or sisters
Athena had no brothers or sisters.
brothers and sisters