1)Arpitan is more a political word, while Francoprovencal (without separation) is more accepted for neutral linguistic usage, even if it tends to be mixed.
2)Retho-Romance languages were more eastwards than westward actually : romand/romanisch is their western expression.
3)For the linguistic situation in Alpine regions, I don't know if a study was made. Germanisation seems to have happen quickly, so it's probable that it preceeded the formation of romance languages (between IX and XI centuries) as it happened in Britain by exemple.
Even by assuming that language = indentity (that the exemple of Switzerland could proove wrong) it's not really sure on which group it would be related.