Yeah, by develop I mean you have to caress, kiss and have sex to develop those stats, every night after you've finished your intimate session with your 2hus they will have an increase in their sensitivity and technique depending on where you've develop them. Keep in mind though that if you stop time to have smex with them they won't develop technique(they're frozen in time lol). Also if you have trouble getting them to bed just try to get their favor to a higher value or maybe you just haven't develop your character enough(by that I mean, getting your skills up, knowledge, speech, combat, etc.). Getting them on dates and spam conversation/skinship and then headpat/forehead kiss/embrace/kiss(or not if you don't want to steal their first kiss without consent, well technically they kinda give you consent but they'll give you their first kiss anyway if you guys have a good date) and go to a hotel after all that, you may or may not be able to take her, just pay attention to the value when it showed you how it was calculated, it'll give you a good idea on how to proceed(if you wanna cheat a bit, just put an aphrodisiac in her tea or food to get the value higher).Though I don't quite understand what you mean by develop, if you mean raising their gems/stats like submission and loyalty then I don't get those stats either lol.
Also if you don't know you can go to option(when you went to bed) and click on the stars on the top of the screen/top row and there will be a cheat menu waiting for you. I don't recommend it though cause it may break your enjoyment of the game.