These can be done from the translation files. So follow these steps:
1. Learn how to translate from this link: https://docs.question2answer.org/translate
2. Define whether you are going to update an existing translation or just customize these particular phrases
3. Create/Update file qa-lang-main.php and add/edit these translation strings:
'in_category_x' => '^',
'meta_order' => '^where',
This will result in posts only showing the category they belong to.
Note: All these steps apply to the whole system, not just question lists. If you want a different behavior for question lists and for the question view page, then you will have to write a plugin for that.