For every recruited friend, you always get 5 gold chocobo feathers. So for recruiting two friends, you'd get 10 gold chocobo feathers.

However, the rewards based on subscription length are given out once. So if both of your friends subscribe for 150 days, you only get the 5 extra gold chocobo feathers for one. Including with the 10 you get from just recruiting them, you'd have 15 gold chocobo feather then.