I have two questions about EU3-DW

I'm playing the teutonic order, starting 1399

1.Through a chain of Event starting with the mission to conquer Riga i controlled finally all Hanseprovinces but i
couldn't annex,vassal or steal them Lübeck their COT. It makes sense to some degree, a trade legue without COT doesn't make much sense but on the other Hand
it's a bit like godmode. Did i miss something or is it now impossible to take the COT of the Hanse&similar countrys?

2.I though about joining the HRE, because i started with sevral of provinces being part of the HRE and my vassal pommeria is part of the HRE too.
I have 200 with the country of the Emp. and my Leader has diplo 4, still i rejected everytime i try to add a province to
the HRE. Did i miss something or does the Emp. just hate me because i took pommeria as a vassal?

That was the right hint, thanks.
Did some "digging" and there is not Hard Threshold, important is the relation to the emporers country.

PS:I can't become the Emporer or diploannex, i'm playing the Teutonic Order and for RP-reasons i wan't transform to prussia, expect the path that forced the Order once...losing power, inner struggle, becoming a vassal....

And for the Hanse, i read that their Cot worked similar as a Capital, they won't give it away as long as they have more then two provinces (Capital+Cot, if they are at different provinces)