1) Use the neighbor's car.
2) Ask the neighbor to pay, in advance
, for taxi rides. You will bring back change and receipts. He/She can be reimbursed by the owners of the vehicles.
These are ways to avoid a "war", but you will be seen as a chump.
If he/she is unwilling to do either of the above:
Rest the responsiblity squarely on your neighbor's shoulders. Politely tell him/her that you have to go out at a certain time. Request that the neighbor contact the owners of the vehicles before this time or you will be forced to have the cars towed. Period.
EDIT: Use this next time.
god i love spoiled college athletes whose parents buy them a townhouse. my fondness of them only grows as three friday nights in a row i have come home around 2 or 3 to find my garage and driveway totally blocked by their friends/teammates/groupies. Last time wasn't so bad, i just blocked their friends cars. yet this time, my car is actually in the garage! But today is the absolute best -- i actually have to be somewhere--and said neighbors aren't sure where their 2 friends belonging to the 2 cars are but they probably will not be back before 10 and they have no keys to the cars. we've gone through this dance before. i don't want to tow the cars -- i cant imagine war with the guys. i'm so tempted to set off the land rovers car alarm system -- then perhaps one of my other neighbors would do the dirty deed?