1. To rename the Portfolio "All" tab please get a child theme from https://vamtam.com/child-themes/ and copy templates/portfolio/loop/sortable-header.php from the main theme to the child (remember to create the missing directories). In the newly copied file replace the text on line 11. Do not change the data-value="all" attribute, just the text inside the <a></a> element:

<span class="cat"><a data-value="all" href="#" class="active"><?php _e( 'All', 'construction' )?></a></span>

2. To remove the Portfolio "All" tab: 

Since the sorting is initialized with JS the easiest way would be to simulate a click on the first tab and then hide the "all" button. Try adding this to the Custom JS Area in Vamtam > General Settings > Custom CSS:

(function($, undefined) {
$(function() {
var cats = $('.sort_by_cat .cat');

How to add custom CSS / PHP code or modify the theme code ?

3. To translate the Portfolio "All" tab please translate the theme's .pot file following this guide:  How to translate a Vamtam theme in other language?