The guests are up to you to bring or not to bring. The number of guests includes you by the way, e.g. 2 guests = you + 1 friend. Also quite often the maximum number of guest isn't enforced (but some guests may end up sleeping on the floor/couch if you go over). In some cases (uncommon), the rent price depends on the number of guests you indicate. Also, in some jurisdictions (e.g., Peru I believe), each guest has to provide some ID to the host by law. Additionally, in some jurisdictions, a tax may have to be paid for each guest (e.g., Lisbon's municipal tax), in theory at least.