Orbs are a number of things and some of those things are far from spiritual. I am not going to suggest that the orbs your friends have witnessed are not paranormal phenomena. It could be that and a combination of the two. One obvious possibility is that the orbs are photographic or optical artifacts. Products of lights unfortunate ability to bounce around and reflect off anything and in terms of a flash picture; or observation using light sources in dark spaces. On the edge between light and the darkness lays the unseen, the unreal and the unknown. More that lays beyond is not yet understood.
Possibility two is that they are not all photographic artifacts and there is a group of people experiencing the appearance of orbs which seem to focus or emanate from a specific place in their home. OK. What's Happening she screamed in the movie Poltergeist. Relax. There are not a lot of people that can tell you unequivocally, exactly what orbs are. We simply can't measure or quantify them in a definitive way. In other words, there are a bunch of theories and more data is always needed. We are left with the evidence of our experience.
I have witnessed apparitions and experience ghostly manifestations as well as some freaky poltergeist activity. Orbs in my experience have been attached to my UFO observatons. multi dimensional probes or alien machines. I dunno. Since this experience is occurring in a house we will assume for the moment it has to do with human history and it's attachment to or imprint on life and the cosmic earth record. OK. I'm good with that. I can only say what they might be.
Without the benefit of personal experience in this siting I can only suggest that there are many ways orbs can be presented to us in material reality. Are they really there? The answer is yes and no. They don't have to be there but you can make them there as a way for you to physically relate to what you are sensing. Our minds can do this for us or to us. I am privy to the experience of a number of people witnessing a specific apparation while others sensed or saw nothing other than our simultaneous reaction to the experience. Why?, another time.
I have experience what some might call an orb which turned out to be a window where I viewed strange landscapes and unique vistas, and snippets of peoples lives. I have seen apparitions made visible to me that where the past experiences imprinted on the space or place. No spirits involved, no presence or entities. Merely a manifestation of my senses producing what I am sensing of the energies of the past. Yes; an orb could be the emanation of a presence whose energy output is not strong enough to manifest fully but as much it is up to your mind to assist the process of emergence into our space time or at least closer in vibration to it. The orb is a piece of a puzzle. or part of a whole.
I think there is no single explanation for orbs. It is possible for it to become exactly what you want the experience to be or it is a true paranormal experience you have to examine objectively and without conclusion. Nothing is just what it seems, there is often more to it. Don't maximize your entities unnecessarily. The simplest explanation can be that there is no explanation, yet.
Love and Light dispelling the darkness
Sim