at 6 months they need to be neutered/spayed ASAP. Do you have a pair of cats? if so, that's good, they are great company for each other.
also, you'd be better off building them a run for outdoor time (cheap and easy, not as hard or expensive as it sounds!) and keeping them in the house at night to keep them safe. If they are wandering off like that they have a very high risk of being hit by a car or poisoned.