Thanks for writing. I certainly can't vouch for anything your father-in-law (or step-father-in-law, whatever) is saying. Obviously I can't know what's going on in his life or in his head.
I
can say, however, that in the Bible there are many occasions where angels spoke to non-believers or where God spoke to them in dreams. Let me list some that come to mind.
[list][*] Gen. 16.7-12. An angel appeared to Hagar to tell her to return to Sarai and to give a prophecy about her baby. We have
no idea what Hagar's spiritual status is, but there's no reason for us to think she's a God-follower. Maybe she is; we're not told.
[*] Gen. 20.6. God appeared to Abimelech in a dream to warn him about Sarah.
[*] Gen. 21.17. An angel appeared to Hagar a second time.
[*] Gen. 40. God spoke in dreams to both the cupbearer and the baker, servants of Pharaoh.
[*] Gen. 41. God spoke to Pharaoh himself in dreams
[*] Dan. 2 & 4: God spoke to Nebuchadnezzar in dreams
[*] Matt. 2.12: God spoke to the wise men in a dream
[*] Matt. 27.19: God spoke to Pilate's wife in a dream
I"ll stop there, because it's enough to answer the question. There are also MANY reports right now that Jesus is appearing in visions to Muslims (by the hundreds), and they are converting to Christianity because of it (
http://encounters-with-jesus.org/jesus-appearing-to-muslims/). So obviously God gives visions, angel appearances, and dreams to non-believers.
That doesn't mean that's what happening with your father-in-law, but it could be. It calls for discernment on your part rather than automatic dismissal of the idea. You're right to be skeptical, but also be open. Try to watch and evaluate wisely.
> Could this be something other than an angel?
We know that one of Satan's main tactics is deceit, and a lot of times he deceives by mimicking God's work. So yes, it could be something other than an angel.
Unfortunately, this isn't a clear-cut issue (where I can say for certainty "yes it is" or "no it isn't").
Does that help? What other questions does it raise? We can talk more about it if you want.