You are confusing different issues, and are trying to tie them together in ways they are not.
The courts don't override impeachment trials and how Congress votes.
If Congress deem Trump has obstructed Congress, and vote him guilty, the courts don't get a say in the result.
Any decisions from courts can be introduced into the impeachment trial, but it is up to Congress to decide the merits and weight of those decisions and how they relate to the impeachment trial.
As for sending witnesses or not, the decision so far is that he cannot invoke privilege to stop subpoenaed witnesses from appearing, privilege only extends to the information they are allowed to reveal. There is no reason to believe that the result will be any different in any other court, as it is a very basic principle relating to what privilege is.
It's just a stalling tactic that Trump is famous for.
Trump withheld the evidence.
Trump had the option to introduce favorable evidence during the investigation, he chose not to.
