These two NON-electricians are gonna work on it. They don’t have the equipment.
Or, IMO, the expertise.
How do you know they don’t have the equipment or expertise?
Because they’re 70+ year old women?
Obviously doing crochet or beads or painting doesn’t mean that they’re adequately prepared for diagnosing and fixing an electrical problem.
But you haven’t said what skills they have (or lack) with regards to electrical work.
I am a “NON-electrician”. And I wouldn’t have any qualms with spending an hour or two diagnosing and fixing an electrical HW heater for my property. (I’ve done far more technically-advanced things than a HW heater even though I am not an electrician.)
You said the heater is new - did they install it?
If not, I agree with another poster - I would have the installers come look at it (assuming the installer didn’t tell them up front “Hey X is going to be a problem. If you want me to fix it I can for $Y.” Which means they already know what the problem is.)