(1) It looks like there may be a conflict with some CSS code on your web page which is resulting in gallery elements being out of position. One possible solution (other than to check your web page for global CSS rules which the gallery might be inheriting) might be to set expandInNewPage="TRUE" (in the Pro Options text area) to expand the gallery on a new page of its own rather than within the embedding page. Alternatively, you could try setting useFullscreenExpand="TRUE" (although not all browsers support the Fullscreen API which this configuration option uses).
(2) Try setting expandInNewPage="TRUE" in your gallery's settings. There is currently a bug (which should hopefully be fixed in a future version of Juicebox) whereby setting expandInNewPage="FALSE" can change the scale of the embedding page on mobile devices. This may be a possible explanation for the problem that you are running into.
Hopefully setting expandInNewPage="TRUE" will fix both of your issues.