not sure on isofix i do hear they are great as fit into car that has isofix my car doesn’t so haven’t even looked at them. i have britax evolva it’s 1-2-3 forward facing….suppose if having twins perhaps look at something that will do from birth upwards…mothercare are usually great regards showing the car seats and also advice…sometime though a little dearer than usual but you could check up north for them too…..best of luck…how old are your twins?