With so many members of the family having the same symptoms, scabies would have to be strongly considered.
Sometimes, eczema can appear like scabies.
You might look for the burrow of scabies. This measures about an inch and will look like a little track. Scabies incognito is a form of scabies in which you do not see the burrow. It is fairly common not to see the burrow.
Most commonly the rash occurs on the lower abdomen, the legs (especially the ankles), the arms (especially the back of the wrists), and the finger webs.
I would recommend seeing a physician for this problem. Be sure you tell your physician that 4 members of the family have the same itching problem. All members of the family should be treated at the same time. Otherwise, they may "ping-pong the rash back and forth. Even members of the family who do not have a rash or itch, should be treated.
Treatment consists of bathing and then applying Permethrin ( Elimite, Acticin) 5% cream to the body from the neck to toes. Wash off after 12 hours of use.
After 24 hours bathe carefully, and change into clean bedding and clothing. Washing, dry cleaning, or ironing of clothing and bedding should be sufficient. You do not need to sterilize.
The treatment should be repeated in a week if there is still itching.
Itching may persist for a few days, or even up to 3 weeks or longer, in spite of the demise of Mr. Sarcoptes Scabei.
I often treat the itching with Eurax, since this has the power to kill the scabies might on its own.
Your daughter or daughter-in-law should be treated with precipitated sulfur 6% due to her pregnancy.
Happy to answer further questions.
We have tried cortizone cream for the itching and washed all bedding and clothing. We will continue to wash everything.