Try to book your seat location in advance through online booking. This will give you the flexibility of getting the seat of your own choice.
Bus journey gets more comfortable in large groups because you spend your time in talking to your known ones. Hence if possible try to get people along with you during bus journey.
In case your family members have not got adjacent seats during automatic seat assignment then make a humble request to other travellers and try for seat exchange so that all of you can sit together.