Inhibitions can only lower, so the only way to keep them high is to avoid "casual" sexy situations. There are 1 or 2 exceptions in the entire game, but they aren't repeatable, and usually are tied to refusing certain events.
As for willpower and intelligence, there are a few ways:
1) Training with Carla in the Bazaar rises HP at first, but after a certain number your health won't increase anymore, raising your willpower instead;
2) If you buy Lea as a slave, she can sing for you and that raises both WIL and INT;
3) If you have become a noble and fixed the mansion's 2nd floor, you have a relaxation room there to recover some WIL everyday;
4) The hypnotist at the circus can increase WIL and INT, but the effects reduce with each use and eventually you start losing stats, so be careful;
For intelligence:
1) You can study at libraries;
2) Lea can sing for you (as mentioned above);
3) The hypnotist can help as well (again, as mentioned above).
These should be the main ways you have at your disposal. There are some items you can use to temporarily boost your stats, but lose some once the effect wear off, and in the next public update there will be some one-off items to increase/decrease INT and WIL as well (although they aren't so easy to find).