Issues with mobile and tablet display

Hi,
I’m really enjoying this theme and love the way my site looks on my computer, feeling almost ready to go live! But I’ve gone ‘live’ briefly a couple of times to check how the site works on my mobile phone and my tablet and there are problems.
Mobile phone – the client carousel appears really huge, dwarfing the other elements of the front page
Tablet – the menu doesn’t work properly – depending on which internet browser I use, it either is too low (bleeding into the layer slider) or the drop down menu is almost impossible to use (it won’t stay visible long enough to click on anything).

From reading some other topics, I see that a common recommendation is to deactivate all plugins one isn’t using, and I’m open to this, but there are a few where I’m not sure whether I’m using them or not.

Thanks in advance for any help!