Lease Provision Against Parties
I have no idea what you mean by having "more than double occupancy in the house" - you say that there are already five people living in the house.
Party Time at bn001's House
There may be state or local laws governing your rental which make the $150 fine unenforceable. There is probably an implied requirement that the landlord's reason for refusing a party be reasonable. But beyond that it is probably largely enforceable (although I don't know how the landlord would verify certain specific requirements imposed by the clause, without haunting the premises on the night of a party).
Does the clause really mean "no more than 10 people, including those who live there", or does it mean"no more than 10 people in addition to those who live there"? Or "no more than 10 people including the resident who is throwing the party," but not including roommates who don't attend? It's not the clearest clause....