is it feasible that i can edit the html from the menus on the top here?

http://yoursdproperty.com/index.php?option=com_content&view=section&id=1&Itemid=27

the house, purchasing property, selling property, etc, wish to have the ability to edit the html. is the fact that possible? where would the file be?

i really need them to consider 100% from the top and also to be spread in this manner that after you increase the menus they'll just get more compact simply because they would always occupy the whole top

Maybe this tutorial can help you: How To Edit Joomla Templates - part 1.

Or read to official documentation for editing templates.