can holly plants be split and if they can when is the best time?

No, they can't, they're a shrub/tree and as such, have a central root. You can increase your stock of hollies by either heel cuttings, or layering in October, and removing the resulting plantlets in 2 years.

Just hunt around near your holly tree and, if it has berries, you are likely to find small holly trees already growing. We constantly have to pull these up but you could move and allow to grow on