It's a fairly bog standard horrible Rover for very little money, highly likely it has some issues that would cost a fair bit to sort.
It's better, possibly. Not really up on Rovers/MGs so can't really help too much. If it's you and 3 kids though, the MG will not be great in terms of space for kids and associated kid paraphernalia. My brother and his wife struggled with her Rover 25 and just the one child (so more often than not used his A instead).
Again, with children that is likely to be a pain.
Something you need to decide/work out is if you need petrol or diesel. For the money you've got to spend, a modern petrol should be a lot more reliable than a modern diesel. The older diesels are more unrefined and not so nice, but are more reliable than modern ones.
Also engine sizes, how much power to you actually need/want etc. no point getting a 2.5l v6 when you just potter about town taking children to/from school. At the same time, if you're mostly using it on motorways etc. then a 1.2 will be horrible and gutless.