Surnames Leffmann, Judell, Kahn, Rendsberg

Hello, I;m new to the list, hoping for some English-speaking contact.

I'm looking for connections with these families, from Hamburg,

Leffmann, Isaac, (b 1829?)
Hannchen Rendsburg, don't know birthdate-married Louis above
Leffmann, Louis(b. 1850), son of Isaac
Leffmann, Rudolph(b. 1889), son of Louis above
            (?siblings to Rudolph; I would like to find out)
Judell, Leopold (b. before 1830's most likely)
Judell, Hermann (b. 1840's), son of Leopold
Judell, Adele(b. 1852), daughter of Leopold
        Adele married Louis above 1882
Kahn, Henriette, born 1848, married Hermann above but probably in USA

I'm in the process of getting certificates from the Archives for Louis,
Adele, Rudolph, but also want to know how I can find out if Rudolph had any
siblings .. .. can someone suggest the best way to find this out?? Rudolph
emigrated to the US in 1908.

Or, also, are there any census lists available for any of the above years??
If so, how do I look these up from the USA?

Thank you in advance for any help!!

Sincerely, Pam in USA