Yes, you can multiclient Isro and SJSro or any other private server at the same time. I speak from experience of doing so.
You can download the client V1.091 from these links, and sadly no there isn't but you can simply use a mediapatcher to swtich between servers it isn't that bad. In my opinion the best Media.pk2 out there right now is from

because it has some level 80 skills, but they're website it offline right now. You can search the forum though there are some pretty good one's out there too.

(Fastest download rate for me.[CLIENT])

(Haven't tested.[CLIENT])
I hope this helps..If I didn't answer something just ask and I'll see what I can do for you.
EDIT: And BTW there is a lot of talk about other servers such as DeepBlue7, ESRO, and other servers but for now we're not sure if they're legit. The only servers that have been online and played by the public are ECSro(VIP),ECSro(NORMAL),ECSro(FEMBRIA), MYSro, and SJSro
-Jon