harada twinsKrad does not interact much with the Harada sisters. But from what we have seen in the anime, he doesn't give a damn about them. He actually tried to kill them both. -very amusing scene- But as for actual 'talking' he hasn't done that at all with either of them… ever. I don’t think he has even given them a thought besides in that scene. So not much to say about them on the anime side.
Now for the manga. Krad does not interact with Riku at all. I do not believe they have ever even been in a scene together. But Risa, on the other hand, was saved from falling to hear death by Krad. Now, this one interaction causes a lot of probems and questions. Was it Krad that saved her? Or was it Satoshi? In an earlier chapter Satoshi was given the ring by Daisukes father to control ‘the other’. It works both ways, Krad can control Satoshi once, and Satoshi can control Krad once. The ring is shown breaking after saving Risa.
What I believe happened, is that Krad did indeed use the ring in the earlier chapter, and Satoshi used it when saving Risa. This is supported by the idea that Satoshi said it didn’t ‘hurt’ nearly as badly after transforming back. I think this says that Satoshi indeed has feelings for Risa, and is able to bring Krad forth as Daisuke is able to bring Dark forth, through love.
To add one more thing, the idea that Satoshi has feelings for Risa is nothing new. He found excuses to go out with her in volume 4, he has also had scenes with her which are quite cute. The development is nothing new, really.
So overall, Krad has had practically no interaction with the Harada twins, but i would be willing to bet that this will change in the future in regards to Satoshi's growing feelings for Risa.