The old Ford Ka's first generation from 1996-2007. Are they reliable as a family car on the cheap for the long term? Road tax prices, car insurance prices, how much it breaks down? Also, is it very reliable on the motorway too? I don't want it breaking down or stopping or something that's REALLY loud on road noise.

They're OK, the main problem they have is rust.
It's pointless saying "An old Ford Ka will be good/bad" because it depends on the individual example of the car in question. If it's been looked after it'll be fine, if not it'll be one step from the scrapyard.

Not a family car at all as they are way to small.
From your desciption of what you need this is totally the wrong car for you.

Too small for a family car, too town-oriented for motorway use for any length of time, and so prone to rust that they'd do so in the Atacama. If road noise is a concern then you're also SOL as they're so light and cheaply made that there will be LOADS of road noise above 50mph, and they're also unstable at speed.

An Escort would be a much better choice on a budget, and the 1.6 would be decent on the motorway without being too thirsty around town, not too bad for road noise, and FAR better for a family car. The 1.3 would be better if it's only occasional motorway driving as it's cheaper to tax, run, and insure.

Depends on your budget (initial and monthly), mileage, and type of driving, so a little more information and we can offer better suggestions.