1. 尽管我住在这儿不久,但是我已经习惯了。
I suggest you use “适应” rather than “习惯” for the first sentence, because “习惯” is usually developed through long time, while “适应” more of your personal “adaptation”.
2. 尽管我住了在这儿这么多年,可是我还没习惯。
The second one: “尽管...还是...” is a fixed structure, so better be “尽管我住在这儿这么多年,我还是没习惯。”
Hope it helps!