Having matching brands of tyres is desirable but this is less important than ensuring the tyres are matching size, specification and type. Some of the tyres already fitted have different load and speed ratings, which is not an MoT failure and not illegal assuming they meet the minimum required specification, but is not ideal. The best scenario would be to replace the front two tyres to match the rears, but if you were to replace just one at the front we would suggest replacing the Pirelli, as this has a lower load rating than the other three.