Hello Tharthan, I would be glad to help you and you don't bother me at all.
The terms you use are different than the ones i know indeed, but it could be because of our different sources and knowledges of the subject. By the way I'm not exactly an expert of sardinian medieval history, so don't trust me too much...
Anyway, as far as i know, the right name for the ones that you call "magiorèndes" would be majorales (it should be written [/mɑː.jˈɔː.ɹɑː.lɛs/] in IPA, I think) o mayorales and they mostly were relatives of the giuighe or belonged to reliable local families. So they where noble people, maybe supposed to be wise but, personally I dont't trust politicians...
In regard to the "magiòres", who I know as majores ([/mɑː.jˈɔː.ɹɛs/]) o mayores, they were more similar to mayors than aldermen, such as the name suggests even in english.
Finally, about the word logu, your definition is absolutely correct, but it refers to a single giuigadu not more than one as you has written (giuigados): the state system were the same but the four giuigados were independent from each other and usually in war. Capitalized, in madieval sardinian language it meant something like nowadays land, country.
I hope I was useful, if yes ask me whenever you'll need.
Adiosu, salude e trigu Bye