Dear VladaFu, it takes me so long to get back here but thank you for your help always!
Proč ne "dvanácti" ?
"Starat se o" is used with accusative.
is svych not a genitive form?
No, "starat se o" requires accusative. "o" is general can use accusative or locative.
Staraji se o svych dvanact ovci dobre??
I understand "Starat se o"
svych = locative (?)
dvanact = accusative
ovci = genitive
Are they correct?
Thank you for your help.
Numbers above four are followed by genitive, so "ovcí". And "svých" is bound to "ovcí" so is also in genitive. "Dvanáct" is in accusative.