The Accord of this age is not a slim car, only marginally narrower than a current Skoda Superb (1840mm vs 1864mm) which is generally considered one of the most spacious non SUV or MPV cars available. I realise that external width does not automatically translate into interior width, but with increases in safety I would expect more of the Accord's width given over to the interior than the Superb's. So without getting both your baby seats into any car you are looking at, or at least getting out your tape measure, there is no way to be sure you are getting a wider rear seat.

Also worth pointing out that some baby seats are wider than others, so regardless of what you change to, maybe look at getting slimmer baby seats. Maybe also think about putting one of the baby seats in the front.

Finally, certainly not suggesting you should buy one, but my understanding of the Mazda diesel's problems are to do with unsuitable usage (for a diesel). If you are doing 30k per annum, that shouldn't be an issue.

How big is big enough? Back seat shoulder room seems to vary considerably, generally the bigger the car the wider the back seat.

I have a requirement to carry three adults in the back regularly - our Subaru Outback was too small for anything other than short journeys, our Hyundai Santa Fe was snug and our present VW Touareg is comfortable but that won't fit your other criteria.

Try Googling for car "rear shoulder room" for comparative dimensions.

When we were fitting three child seats in the back, we found the Mondeo was one of the better family cars to hire.