@Aline283 First of all, there is no way that a new host should accept a 3 month booking. If the guests turned out to be horrible, you'd have a big hassle on your hands. New hosts should stick to short bookings, 2 weeks, max or even one week, until you are more experienced with vetting guests and being a host. It's a big learning curve, both dealing with guests as well as Airbnb. And anyone who stays more than a month will fall under landlord/teant laws, and that can get messy.
Next, do not accept 3rd party bookings. Not only are they against Airbnb's TOS, if the guests cause problemes, Airbnb will not back you up. It's very common, also, tht when someone books for others, they don't convey any of your houserules or other things to those they are booking for, which can cause you no end of problems.
There are 3rd party bookings allowed if a host has a business account, but I don't know how you determine if the guest has that type of account.