Please advise if "Welcome to the White House" an imperative sentence? Is that normal to say: "Welcome to here"'?
"Welcome to the White House" is not an imperative.
It is an idiomatic expression roughly equivalent to "[We / I] welcome you to the White House", which is a declarative sentence.
The imperative would be something like "Welcome everyone to the White House", which means something like "Make everyone feel welcome when they come to the White House".

"Welcome to here" is impossible. To mean that we just say "Welcome!" and nothing more. "Welcome to my home" or "Welcome to our home" and many similar expressions are possible.

Hi Cj:

Thank you very much for your reply.