how to handle multiple ajax wordpress queries?

If you have a form you should have a sort field in it, so that you can send your order value on form submit. This way you can send the sorting parameter to your backend callback function.
If you don’t have a form you shoud add this parameter to another element with a data attribute like that:

<button id="load-more" data-order="DESC">Load More</button>

And then in your javascript code add this value to the ajax call parameters.

Remember that you should change this parameter when you call ajax for sorting.