I know you're concerned about getting into the house, not the doctor himself. I said he has something to discuss with you even *if you don't have Lohse*. Which means even if you don't have Lohse, he should still let you in. I probably should've put "even" there in the first place to make it clearer.
Granted, I can't say anything more concrete than this. This is based on what I have heard, and I also believe they won't block off the entire encounter with this character just because you don't have Lohse.
What was that quest you mentioned, btw? Was it the Justinia/Isbeil quest?
EDIT: After a bit of testing, I have to admit, it seems the only way to enter his house is by having Lohse in the party. After talking to the door for the first time, the journal does say "it seems the door only opens for Lohse". The other way to enter his house would be by using the barrel by the beach. And that barrel cannot be replaced by a generic barrel. So.... I'm afraid you really can't enter his house. Unless there's yet *another* way. Sorry about this, anyway.
Last edited by Try2Handing; 15/10/17 10:28 AM.