If this is a test and you must use future perfect for one of the gaps and future perfect continuous for the other gap (and can't use any other tense), then there is only one correct way to do this. The key word in the sentence is BEFORE. Both actions in the future but one is finished before the other begins. SO... We will have rested for three weeks BEFORE + the next action begins (at the future point in time) BUT will not have finished, SO...we will be hitting the road again. Yes, it is a little unusual because we often use other ways to communicate this concept, but we use it when we want to focus on the point in time in the future. So you may see a conversation like this: A: Won't you be tired on the second leg of your journey? B: Not really, we will have rested for three weeks before we will be hitting the road again (often we use 'will hit' or just 'hit' in the second part of the sentence)

I would say "We will rest for three.." "before we hit the road again" Any other way sounds weird and over complicated.

Hi Aliona, Are you able to post a link of your test for us? I've searched for the question, and the result asks for only present simple or present continuous. www.eflbooks.co.uk/samples/9781108564670.pdf (Page 1, Question 2) I think Chris has given the best answer, but I wonder if the test-writer has been "too clever" with grammar. I agree that the natural answer uses clearer, simpler grammar.

will have rested ... will have hit... i think, the sentence it's a bit strange

Completely depends on context. If you are planning the trip, you would say "We will rest for three weeks before we hit the road again." If you are discussing different travel plans, and want to emphasize just how many weeks of rest each plan has, then you would say "[According to plan B] We would have rested for three weeks before we hit the road again." That is, in plan C you would get only two weeks. Plan D would give you four. And so on. If you don't have any other clues, I would choose the first sentence.