I can't really rule out any of those options, but the discrepancy in situations and people present makes it difficult to blame any one person for all of the events. (The key event in particular occurred with my girlfriend and brother present, while my sister was out of state. And the event with the sonograms occurred when I wasn't there, so not even I am a common element in all the weird events.)

I'm leaning towards a mixture of #2 and a fourth option - that there's some environmental condition in the house which is causing people to behave oddly.

An important qualifier in my post is that I previously regarded the idea of haunted houses (again, without prejudice for the word "haunted") as purely fiction, entirely in the heads of the occupants. I'm now forced to conclude that there are houses where - for whatever reason - strange events are indeed common.