can anyone help? thanks a lot!!

Douglass's and Williams's. Examples from Chicago Manual of Style, 15th ed., 7.18 include: Kansas's legislature, Burns's poems, Strauss's Vienna, Williams's reputation.

Douglass returned with funds to purchase his freedom and also to start his own antislavery newspaper, the North Star (later Frederick Douglass's Paper), which he published from 1847 to 1860 in Rochester, New York. The abolition leader William Lloyd Garrison disagreed with the need for a separate, black-oriented press, and the two men broke over this issue as well as over Douglass's support of political action to supplement moral suasion. Thus, after 1851 Douglass allied himself with the faction of the movement led by James G. Birney. He did not countenance violence, however, and specifically counseled against the raid on Harpers Ferry, Virginia (October 1859).

from Encyclopaedia Britannica, 2004 DVD

The Archive can also help.

Treatment of possessive singular s is variable. There's no one right way. Most common in the US is to add 's to mark the possessive after all singular nouns except Greek names ending in -es. In English, as in German, it's wrong to add an apostrophe to form a plural. And you'll notice in #3 that Harpers Ferry is spelled without an apostrophe. That seems to be standard, though you'll also find Harper's Ferry and (on the park web site itself) Harper Ferry.