I've just had my patios and path redone op. It took between two and four men six weeks. But they are huge. But I have a sense of what's involved. For the job you've listed you should be looking at at least seven grand, likely more.
So they need to grind out existing mortar.
Remove the existing stone.
Escavate the current base
Dig out the foundations.
Lay the new base, ideally with compacted aggregate or similar and likely concrete edging.
Relay the stone on its sand bed.
Joint rhe stone.
Then they need to dig up the existing path.
Dig out the foundations for the new one.
Lay the new path.
Mortar between the bricks.
It's a huge job. That will take significant machinery, from diggers on.
And if it's not done properly the problems you're going to have in a year or two can't be under estimated,
Even if they do use a concrete base, the angles need to be then built in and sloped enough so the patio drains away from the house and into the garden ,,not ideal for it to run off and cause muddy surrounds, but if they did take that route it's going to take them piping in the concrete as there will be so much required,
All in I don't see how this can be done for 1400 quid and in a few days, a few days is feasible with a big team, but the men need to be paid and it's going to cost more than 1400 quid.
Overall I think your husband is right to be wary, don't do this unless you know you've got a reputable company doing it, and get a few quotes in.