だという

[MeitanteiJesus]

In the phrase: 父のものだという書斎は綺麗

Is it parsed as:

父のものだ /// という /// 書斎は綺麗
The study that is said to be the father's is pretty.

OR

父のもの /// だと いう /// 書斎は綺麗
This study that may be the father's is pretty.

---

I wonder because the context of the story prior to this line makes it seem that he is uncertain if this is the father's study.

Yet the second option seems kind of farfetched as I'm not too sure if だと いう can be properly translated as "may be". I know だと can mean "If it is the case", but という seems more correct to me, and in that case, is the だ simply acting as です mid-sentence？

[NileCat]

Semantically speaking, those two are the same. The fact that you only heard someone say the study is your father’s means that you don’t know the truth. The nuance/degree of speculation or doubt would highly depend on the context.
Grammatically speaking, they are the same as well, because you can parse it as 父/の/もの/だ/と/いう.
Practically speaking, however, the former seems slightly easier to understand.
（＜父のもの＞←だ＝である＝です）　←という＝と、言う（と、言われている／と、言われた／と、聞いている／と、告げられた／と、信じられている／として知られている）書斎

[MeitanteiJesus]

Thanks, if という = 信じられている depending on context, then it definitely makes sense now. I'm really starting to see how contextual Japanese is!