Yes, you will have to do that as well. By default, the WeeWX skins do not have provisions for the myriad of different sensors that a weather station can come with.
Most likely, the extra humidities are appearing as extraHumid1, extraHumid2, and extraHumid3 in the WeeWX data stream. You'll need a database schema that can accommodate these new types and store them (the wview schema has extraHumid1 and extraHumid2, but not extraHumid3; the wview_extended schema has all three).
Then add the new plots to the skin.conf file of whatever skin you are using. For example,
[[[dayhumidity]]]
[[[[outHumidity]]]]
becomes
[[[dayhumidity]]]
[[[[outHumidity]]]]
[[[dayextrahumid1]]]
[[[[extraHumid1]]]]
and so on. This will cause plots dayextrahumid1.png to be generated.
Finally, you'll need HTML tags <img ... > to display them.
-tk