Is it possible to add two quizzes under the same hint?
You can only create a single quiz per clue.
But if you’re using a ‘treasure hunt’ (i.e. sequential, which is the default) format, you can put an additional clue after the first one that does nothing but present a quiz, and then the two quizzes will happen in succession. To do so, when the camera viewfinder appears for the second clue, tap Change Clue Type at the top right, and then choose Skip Clue.
To see all the options for creating more flexible hunts, see here: What can I do with a Klikaklu hunt?
What about writing URLs - Do they appear as clickable link?
Yes, they do.
Also, i’s easy to see how a hunt will work in practice. You can do a test run before you save it. You can also save a hunt, play it as yourself, and then delete it later if you wish.