Proper fasteners for Post/Beam/Joist intersection
I agree with @JimStewart , notching can be dangerous. Go to your local lumberyard and order a Simpson Strong-Tie column cap similar to this one:

https://www.strongtie.com/boltedcolumncaps_columncaps/eccl-ccc-cct_productgroup_wcc/p/eccl.ccc.cct

You can order them for 3-2x10 built-up beams on 6x6 posts with 2-2x8 beams joining the 3-2x10 beam. Also, you can order a corner connector.