Usually it’s better to release one at a time, otherwise they are all likely to scarper and none of them stay around.
Remove the pen as that won’t encourage them to come back. Spread the houses out as they won’t want to be near other hogs and don’t put food too close to the houses. Site the houses somewhere so the entrance is away from prevailing sun/wind/rain
Some of the females may decide to hang around in your garden but the male will likely leave as soon as he’s had his way with the girls!
Then it’s just a case of providing food and water regularly.
Let me know if you need anything else