The code for carousel vertical is in templates/property_pictures3.php file.

Images are resized using these resize rules: listing_full_slider,  listing_full_slider_1 and wpestate_slider_thumb

To remove the resize rule for images must edit templates/property_pictures3.php and replace above resize rules with full.

Next must add below css in Theme options – Design – Custom CSS ( help:  https://help.wprentals.org/article/3029/ )

.carousel-inner .fancybox-thumb img {
height: 337px!important;
width: auto!important;
}

@media only screen and (max-width: 840px){
.carousel-inner .fancybox-thumb img {
    height: auto;
}
}

@media only screen and (max-width: 568px){
.carousel-inner .fancybox-thumb img { 
height: auto!important; 
width: auto!important; 
} 
}

.single-estate_property #carousel-indicators-vertical li img {
margin: 0px auto!important;
float: none;
left: 0px;
right: 0px;
display: block;
}

#carousel-indicators-vertical img {
    width: auto;
    height: 83px;
}

.single-estate_property #carousel-indicators-vertical li img {
    margin: 0px auto!important;
    float: none;
    left: 0px;
    right: 0px;
    display: block;
}

.single-estate_property  #carousel-indicators-vertical li {
    background: #323a45;
}