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No. 1 & 4 >> they are the same. Not 达 but 達, though.

私達はまだ友達でいられそうですか?

More firendly expression is:

私達、まだ友達でいられそう?

or

私達、まだ友達でいられるかな?

Actually, number two is not the best because you wrote tsuzuki suru, when it should be tsuzuku (it's a verb, you don't need suru).

Can we still be friends?

Yuujin mada iru no koto ga dekiru no?

友人まだいるのことができるの？

And yuujin is more familiar. Tomodachi does mean friend, but yuujin is more intimate and implies you are pretty good friends.

I have certain friends, my friend KK I've known since I moved to the US, so she is my yuujin. My friend, Osha, I've known her for a long time, but we are not close, so I call her tomodachi. See the difference.

And if it wasn't for Soph, I probably wouldn't have realized you were using tatsu for tachi.

Tachi- 達 "plural suffix"

Tatsu- è¾¾ "smooth"

Number 2 is better. it follows correct japanese tenses.