For a guest refund - it can be given by airbnb (according to their guidance ) if your place 'does not contain clean bedding and bathroom towels available for the Guest’s use'.
The guest should 'within 24 hours of check-in to document the issue and place a hold on the host's payment. Include photographs or other evidence of the issue as part of your claim.'
However the guest must ' Have used reasonable efforts to remedy the circumstances of the Travel Issue with the host prior to making a claim, including messaging your host on Airbnb to notify them of the issue. We'll verify this in your account'
First of all, you should call airbnb to discuss this with an agent. I don't know all the details of what happened, but did the guests follow the policy ? - ie tell you it was an issue via a message. You can also ask airbnb to let you see the photographic evidence that should have been sent to them. Also I see your reviews all mention your place is 'clean'. The guests stayed for the full duration of the stay and I think that should be taken into account. If there was such a big problem, why would they stay so long.?
It sounds if airbnb might made a decision without consulting you and perhaps without paying heed to their own rules, so it is worth to question it and ask for this decision to be reappraised based on the policies.
As far as the early check-in and late check out, unless you make an agreement in advance to this, you can say no.
In my opinion arriving at 6am , they should have booked the night before as well.
Good luck and let us know how you get on.
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