Here's a question that has pestered my mind for a long time now about Roman-Catholicism spreading into outer-space with aliens:

Unknown.

Does grace and salvation apply to angels?

It would depend on if the aliens have souls and if they acted contrary to God's will which is what sin is. Angels acted contrary to God's will but they do not have souls so they cannot benefit from salvation. Animals do not have souls but also don't really have the conscious free will that humans have to decide to act with or against God's will. That being said grace is the spiritual gift that allows you to unite your will more with God's so it can only benefit those with both a free will and a soul. So to answer your question, ( or not) I have no clue how aliens would fit in to the equation.

Soul means being alive. Anything living thus has it.

Free will was granted to Eve and Adam by the Serpent, not Yahweh. Christians call that original sin.

Because animals did not disobey by partaking of the fruit of the tree, and do not sin for pleasure and gain like humans do despite an endless parade of religions and Gods commanding them not to, they won't share this grace, but condemned humans cast out of Paradise for it will? How nice.

Soul means life, so if they're alive, yes, they're alive.

A Messsiah is supposed to liberate the Judeans from an occupying enemy. Unless aliens are in such a situation and Jesus can do what He's going to do for the Jews one day thousands of years in the waiting, that question is irrelevant.