This is not the opacity of background images, but overlay. You can override it through CSS.
Determine through the browser code inspector this item, override the code and insert in the custom.css file.
For example
The code for override will be such
.sppb-addon-articles-layout.layout-arabica .leading-item .sppb-addon-article::after {
background-image: none;
}
As for the slider, there is a setting for this.
Also how can we delete the bookmark option on the slider
It must be a specific type of content inside the slider. Replace it on your own. I have not used this template and I can not say for sure.