+ Regarding first problem on this link: http://www.nmbt.org/joomla/ image in second slideshow not found: http://www.nmbt.org/joomla/images/jaslideshow_home/nmbt-flyer-front.jpg
+ For the second concern: http://nmbt.org/joomla/index.php/the-tour this is not an issue of JA Slideshow. When you add an image whose dimention is bigger that size of slideshow, it will automatically scale it to smaller size to fit slideshow. However, this will not happen when you add an image with smaller size, it will use original one instead.
Ex:
Original image: http://nmbt.org/joomla/images/TourPhotos/_MG_2439.jpg
Scale Image: http://nmbt.org/joomla/images/resized/images/TourPhotos/_MG_2439_471_706.jpg
If you want to show center image on slideshow. You can try to do as below
Open modules/mod_jaslideshow/assets/themes/tiris/style.css file
From
.ja-slide-item { left: 0; right: 0; }
Change to
.ja-slide-item { left: 0; right: 0; text-align: center;}