You must have done 3 take offs and landings with 90 days of the day you carry passengers so if you only did one take off and landing on each of the dates you would run out on 18th Oct as you suggest. To carry pax you have to go and do 3 take offs and landings, either on your own, or with an instructor.
As there is no such thing as P2 on a single pilot aeroplane a PPL holder carried on board can only be a passenger so the 90 day rule applies. If they held a valid instructor qualification you could do your 3 T'O and LDGs or, if you hold an instructor qualification and the other pilot is a student then you could do it. In simple if you don't qualify as crew, you are a passenger.