Do your parents have their own solicitor?
If yes, have your Dad call them and see what provision they are making for clients in the current circumstances.
Most solicitors will take instructions over the phone and will travel to clients ( while social distancing) to have the will executed or, alternatively, will set out the protocol for neighbours or friends to witness.
If your parents don't have their own solicitor, do any of their offspring have one? In which case, have them make that call.
If you are one of those families who are non-litigious (and there are some out there)- at worst, on the death of either parent, the offspring can deal with the deceased's estate by disclaiming any share on intestacy.
mf