October to December is the ideal time to visit Bhutan as the air is clear and fresh with sunny skies
Since you are a big group I would suggest that you book your flight tickets in advance.
Also check booking.com for hotel booking
Happy Holidays !
Spring : March, April, May Nature lovers who are keen on local flora should consider visiting Bhutan end of April or in May. Flowers would be in full bloom then. Another high and crowded season for Bhutan is September, October, November. October - November is the peak time. Since you are all age group, opt for a time before summer start and yes also go for a package / pre booked tour