I think that old man is our Mister Farmer/Breeder's grandpa, who's old, deceased, and gave his estate to his grandson.
Dosu who doesn't get Darwin Award can live longer than human, and they're not really the most perceptive being about time. For them, everyday just repeats itself with death as "something that happens another day".
When the shithead dosu said, "other Dosu," it actually means the other Dosu. There are, apparently, other dosus with other clans around these mountains.
This shithead one has gone around and killed them all off, gathered their herds, and is leading them all.
Yu-Yu-Yuu-The other...? What did you do to the other Dosu ze!?We don't need useless Dosu who can't let us take it easy je!! Useless!!Nitaa
(lit. "grin")You don't know je? This Great Marisa killed them all jeWhy would you say that ze! Why is everyone so cruel zeIf you don't understand, take a look around youThere's not a single Yu who will stand by your side je
hehehe...Now... you will disappear like the other Dosu jeThat Dosu is more befitting for our leader!