@Dan164
Everyone's idea of shady behaviour is different. The only thing I can see that they are doing wrong is not picking up dog mess? You should ask them to ensure they do so.
If they have paid for the 3rd person you don't really have any right to meet with the person or demand that they are there for you.
As for going away for 3 days - I really don't see why this is shady (unless there is more to this). People anywhere for a month may go on a trip, visit friends, etc...
Sounds like there must be much more to this than you are saying as if you 'evict; them on the grounds you describe then you will find that AirBnB sides with the guest and provides a full refund.