De-registering vehicle can only be done in person at the traffic department by the registered owner or legally assigned proxy (in the case of a company) or the executor of an estate (in the case of a death)
Considering your circumstances, you may be able to assign a representative. I suggest you get in touch with the department of transport offices and take it from there.
You can however cancel your insurance without de-registering the vehicle and in your case, it will be far easier to sell the cars to a company that handles all the paperwork and change of ownership for you.
You will not be able to get hold of any government offices right now considering the Covid lock down.
In the meantime, get in touch with companies like CarZar, TheCarBuyer or WeBuyCars, they might be able to advise you because they deal with paperwork on a daily basis.
There are also private companies that specialize in vehicle registrations and licensing, they will not be able to scrap the cars for you, but they could point you in the right direction.
Here are a few of these services: