On the Cardigan area, I wrote a bunch of stuff in reply to a similar question about Pembrokeshire and Gower a few days ago if you can find it.
I lived near Cardigan years ago and got to know the countryside very well. There isn’t the jaw dropping scenery you’d get in the lakes but there are areas of great beauty that slowly work their magic, pristine beaches, etc. Well worth a visit.
I’ve camped when the kids were small at Cardigan camping and touring site just off the a487.. lovely place, working farm, and tje friendly farmer invited little kids into the tractor for cab rides.
If you can find a campsite near poppit sands, that would be a great location. There used to be tents/campervans in the fields above the cafe there but that might have ended as I can’t see anything on Google.
Preselli hills are the only obvious option for MTB, and it’s only a relatively short loop, but I enjoyed it the couple of times I did it. Lots of single country lanes for roadies. Otherwise you’re about an hour’s drive from the Cambrian area which has some of the best- elan valley, doethie valley, etc.
I’m heading out there in a couple of weeks, can’t wait