The catfish should be fine, IME gars and gar shaped fish (needlefish, pike characins etc) have trouble swallowing stocky fish like catfish and cichlids preffering to go for more "fish" shaped prey like goldfish and barbs. What i would be worried about is the ammount of bioload being placed on the tank and filters. The gar is only about a third of its eventual adult size and the cats will reach at least 2 foot when full grown, to house them all together your friend is going to need a 180 gallon tank now and be upgrading to a 500 gallon tank or indoor pond in the near future.