php – How to display a woocomerce group product correctly?

I am building a Woocomerce site with the GIOIA theme and it contains a grouped product named “Ensemble Wendy”.
As far as I know, grouped product in Woocomerce should be displayed like this : it lets you choose all the options for the childs products and lets you add them to the cart in the same page.

Unexpectidely, mine looks like this: it shows buttons witch links to the child products’ individual pages with no option to add anything to the cart.

I have checked Woocomerce’s official documentation for grouped products and apparently I don’t thing I have done anything different from what’s in the tutorial so I am confused.

I searched in Woocomerce’s settings as well as in the theme’s setting but I didn’t find anything who could correct the problem.

I searched for solutions online and I found a plugin called WPC grouped product which normaly should give the result that I want but I get this instead: the child products are displayed but there is no place where I can choose the variations for the products and this prevents me to add them to the cart. I inspected the page with the Inspector though, and there seems to be a select element there but it’s hidden. I’ve searched everywhere in the settings if I could find anything to correct that without success so I decided to force everything by just overriding the css with a custom code :

.woosg-products .woosg-product form.variations_form .variations .variation .select select {
    display: block !important;

And then, it displays the result I was looking for and finally allows me to add something to the cart.

Now the problem is that, after I select some options and Add them to the cart, the grouped product seems to be successfully added but it hasn’t retained the price or any other information about the product : Here is a screenshoot.

Maybe there is a way to correct through code but I am still not good enough to touch a theme’s code source yet.

I’ve looked everywhere if anyone had a similar problem but I didn’t find anything helpful.

Thanks for anyone who would help me.

Edit :

I already posted that question in stackoverflow and I think it may be kind of off-topic there so I reposted it here. I am still new to stackoverflow and stackexchange so if I am doing anything wrong, please tell me.