Having great difficulty removing them to replace the discs. Soaked them several times with a penetrating fluid, got as big a lever on them as I can and tried hitting it with a mallet and tried heating them up.

Now stuck with what to do next, any suggestions?

Try turning the wheel on full lock and use a long breaker bar, also using six sided socket are better for cracking off tight nuts.

I used an air get on mine first then a long bar for leverage, it was a pain in the arse but I remember tightening then loosening after penetrating spray and heat.

I use a long bar and a 6 sided impact socket. Sometimes I sit on the ground and use my legs.

 

Make sure you are going anti-clockwise - Sometimes when looking at a fastener from the wrong side I've been tightening instead of loosening.

Turning full lock allowed me to get a longer bar on to loosen the bolts. Fairly impressed with how tight they were. Did the same on my dads mondeo a few weeks ago and they have loctite on the bolts, but were nowhere near as tight.

 

Thanks for all the above suggestions.