I think Natsumi and Hosei don't reply to their followers' tweets to them.
I dunno about Natsumi's but Hosei is actually very interactive with his followers. Twitter has moved "replies" to a separate feed than the default when you visit peoples profiles for whatever reason:https://twitter.com/tukiteihousei/with_replies
Sometimes people will say to him "Housei, it's my birthday! Please reply" and he'll reply with "Yatta~jan" (something like that, it's a catchphrase of his). Once or twice he's also done a "Ask me Anything" or other thing and replied to as many as he could etc. http://yamasakigifs.tumblr.com/post/839 ... n-and-thishttp://yamasakigifs.tumblr.com/post/844 ... witter-fun
Another time he did a "Guess where this photo is from" after filming on location for the Drive A Go Go travel show and those who got it right he tweeted a "Congrats!" message to each of them. A few people have tweeted art or pictures they have made of him and he has retweeted/thanked them. I also liked this piece of advice he gave to someone worried about workplace pressure:http://yamasakigifs.tumblr.com/post/565 ... saki-hosei
I don't think he can reply to all messages of course though.
Could be wrong, has anybody tried to tweet to one of them??
It would probably be best to do so in Japanese out of respect to the native language that all their tweets are in. Housei has studied English to a certain level but I don't know how much he would understand. I did once reply (in Japanese) when he was asking for help on how to post video clips online but so did many others (he thanked everyone and said in responce he was gonna figure out how to post a video on Facebook but I guess he gave up on that lol... I wish the Gaki crew would do Youtube).
One day I wanna tweet to him with a piece of fanart, art can be understood without language barriers after all, but haven't got the time yet. Maybe I'll get a reply, maybe I won't but whatever it'll be a gift