I am not that familiar with restaurants in the precise area you describe but if it helps there are two just slightly further afield to the west of Caerphilly I can strongly recommend on the basis of consistently satisfying experience - both have a great setting and great food:
We've had a few successful family gatherings at the Fwrrwm Ishta in Machen. Their vegetarian options are a bit lame, but thats not going to bother most people. They have a pleasant conservatory area which is particularly suited to larger groups. http://www.fwrrwmishta.co.uk/
Thank you for your suggestions.
Jim: I think the restaurants you have suggested are a little too far away for us, as we will be taking a taxi (not brave enough to rent a car and drive!)
Pam and Purple: I have been to both of these places before and had excellent food. In fact, I was at the Fwrrwmishta 2 years ago when I visited and enjoyed it. I couldn't remember the name though. An uncle took me to the Hollybush about 5 years ago, but we ate downstairs in the pub not in the restaurant. Have to say the food was delicious anyways!
I have untll the beginning of November to make up my mind and try to make all the arrangements (not easy from Canada). So, please if anyone has any other suggestions they would be very welcome.
Travellers rest, Caerphilly Mountain - may be of interest
Been there many times, very popular.
Also, been to Black Cock many times.Edited: 3:07 pm, September 22, 2011