Great questions! I'll work through them in order:
Is the family tree available to all? Should it be included in the character envelopes?
It is available to all. You can put it in the envelopes if you like (maybe on the back of the cast list), or you could just fix a few copies up on the walls at the party.
There are one or two people who are interested in playing, but English is not there first language and are afraid that they won't be able to keep up with the flow. One of them suggested that the two of them play a single character. That way they could help each other with the words and such. I'm not sure if that would work, but I was thinking that I could assign them characters that work together anyways. One is female and the other male. The ladies english isn't too bad, although the guys is a bit lacking. They seem so eager, that I'd feel bad if they couldn't join in.
Mm, I'm also not sure if it would work for them to play a character together. Let me come back to this one, I'll give a proper answer when I've thought about it a bit.
Can anyone tell if the diamonds are real or fake, just by a rock-paper-scissors test? Only certain ones?
Anyone can tell.
Does blood need to be taken some how for a blood test to be done?
What if a player doesn't understand the importance of the blood groups?
When you give a player the results of the test, ask them if they understand the importance -- if they don't, then you can explain it to them then.
Should the first aid kits have a comment directing the user to the waiter?
Yes, they should I think, that's a good idea! We'll add that.
Should the players have watches with them? Should I be timing interactions? Is it all just a general feeling?
It's just a general feeling really, it doesn't have to be precise. (In our more recent games we just say 'talk briefly to someone' rather than a specific number of minutes.) It's good to have a clock or something generally visible though, so people can have an idea of how the evening's progressing.
Are arrests announced to all? Is it kept quite?
That's up to the person doing the arrest -- they can choose to make it as public as they can, or to try and keep it quiet. Of course, if the person being arrested protests loudly, then it will probably become public anyway.
Is the prisoner removed from the room until the evidence is heard?
No, they can stay in the room and continue interacting with the other players, they just lose their ability cards.
Is it only presented to the waiter?
Does X need to announce that they are an FBI agent before arresting someone? [NB I've removed the name here and in your post above, in case any players are reading this!]
Yes (and show their ID badge), to the person they're arresting, but they don't have to announce it publicly.
Would I be able to get character list, and character info, in a non-pdf file to allow me to add the info and names for the new characters.
Yes, sure -- if you email me (click on my name to the left here) so I have your email address, I can send it to you. Is Microsoft Word format OK for you?
Also, I purchased the game for the hostel that I'm staying in. I was wondering if it would be okay for them to use it again, when I'm not here. They're already reimbursed me for it.
That's absolutely fine, as long as they don't charge people money to play in it. (If they want to do that, they would have to pay extra to upgrade to the commercial license for the game.)