I cannot imagine what you are going through. My wife, who passed away six months ago, while suffering with a form of dementia for six years, was never into social media. She, and I, both had/have cell phones - but not smartphones. So...I never had to deal with the problems of internet and social media interactions while caregiving for those six years. Maybe, if at all possible, you could confiscate your husbands phones, trade them for a simple cell phone without all of the high tech. options. Come up with some excuse as to why they are no longer able to access the internet - (Supplier no long provides it or some such nonsense.) Might cause a temporary problem, depending on the level of husband's illness, but may just solve the problem.
Good luck, hopefully you are able to resolve this problem quickly - but is you are not able to resolve it - However, be patient, it will pass - and a completely different phase will have to be faced. Stay strong, provide a lot of love and attention, you will never regret it.