Those games are not connected in this way, unnamed is not a sequel to the unseen. Stories are different, and those games can be played separately. Also unnamed is more action based game and unseen is mostly about the story (and some choices like in all Visual Novels).
Unseen and unnamed are connected only in a few loosely references. And maybe general story idea (message).
About that unseen order e-mail Der Luchs (Sascha) and ask when when he will receive next part of the Cards for the remaining unseen releases. More questions he will get on e-mail the faster he might do it.
Ok I will spoil it, since you guessed it correctly If people will like unnamed, and when I will be fresh for new work... the third one called unknown will be created. I have it in mind already
gambler172 >> unseen is not an easy game, but it is not harder than ordinary Visual Novel. In the manual you have info what endings you can expect, and some small hints