For 1 ticket 2 persons are allowed and the extra person is allowed by payment, may be rs100. Usually they ask couples to participate in this.
We had participated in this 2 years back. Both my children were allowed free and they were seated in the side stone bench (or mandapam), and for my mother - in-law, we bought a token and she was seated outside the grill at the back of this area where kalyanotsavam is performed.
I don't know whether small children are only allowed to sit in the side of kalyanotsavam hall or big persons also.
In your case, it will be appropriate if your parents perform and you sit in the side.