Airport personnel are bothered about visa validity only, as the visit visa is only one month valid from the date of arrival, they ask within that period only. Even though it can be extended for 5 more months.
Better you book it within one months time, later once your family arrives here, either you can reschedule it or cancel it. Its upto you.
But to be on a safer side, hurdle free journey my suggestion is to book within a month's time.
If your family is coming alone, I mean without accompanying any males, it will be a harassment, I hope you know government officials....