Christmas is not an official holiday in Thailand, but they close for New Year. If you are staying in a hotel it is easy but if you're staying in private accommodation you will need a TM30
If you adopted her children you can stay on a visa based on Thai children but that stops at 20 years old. So as her children are in their 30s you will have to convert to a retirement visa or leave Thailand.
I've seen this question raise over the years on numerous forums and it has been established that minor maintenance work in and around your family home does not constitute work.
You need to check what the requirements are to leave PH as your government have specific requirements for citizens travelling to Thailand. I suggest to join PH Thai group on FB