Can I fit 3 guardian fix pro 2 seats across the middle row of an Smax?

[Linguaphile]

We've got 3 under 4, and the guardian fix seemed to get great safety ratings and also has good longevity. Just wondering if they'll fit into our smax?? Anyone have experience who can advise?

They might fit, but not sure you'll have enough room to get your hand down the side to be able to strap the children in.

The guardian fix is one of the narrower car seats though

I suggest you head to a Kiddy retailer and ask them to try the seats in your car. They won't have several Guardianfix seats, but most have the full range of Kiddy seats, and by doing a bit of measuring you can see whether three would fit. I agree with Twojues that the Kiddy seats are some of the narrowest at the base.
The newest seats - the Phoenixfix 3, and the Guardianfix 3 (which is about to arrive in the next few weeks) both have sliding isofix bases which mean you can push the seat sideways out of the way whilst you do the seat belt buckle up, and then you can slide it back into position after. I haven't tried it personally, but it could resolve your problem if you can get the centre child fitted first.