Hello and welcome to Connect @cateye13. So very interesting. What a head scratcher, your family having hand tremors, and your pet, too. Are you all under a great deal of stress or stressful living conditions by chance? How long have you lived in the home?

For you, given your chronic pain from fibro, tremors can be symptoms from Central Sensitization which is an umbrella to conditions like fibromyalgia, neuropathy, migraine, IBS, TMJ etc... Here's a pretty extensive government article from PubMed Central about central sensitization:

Central Sensitization: A Generator of Pain Hypersensitivity by Central Neural Plasticity
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2750819/#:~:text=Central%20sensitization%20corresponds%20to%20an,efficacy%2C%20or%20a%20reduced%20inhibition

Working with a neurologist will help pursue necessary testing and rule out other potential underlying cause or conditions. I hope you get in soon (cancellations happen)! CSS is sort of the final straw when everything else is off the plate and docs have no more answers. Even doctors can be unaware of central sensation which is why I like bring attention to it here, just so folks are aware that it could explain the unexplainable. Will you please keep us posted? Wishing your whole family well.