How to widen deck past beam
I’d remove the last two existing joists (joists furthest from the house) and reinstall them next to the third joists. I’d fasten them together with 1/2” thru bolts at 8” o.c. Staggered 16” o.c. Top and bottom. (Install them 3” from the top and bottom 

Then I’d install a 4x12 across the end of the deck (extending it to the existing width at each end) and align the top with the top of the existing beam. I’d fasten it to the existing beams with Simpson GLTV beam hanger (installed upside-down) at each end. (Be sure to order it the correct depth based on your existing joist depth.)

Then I’d install the same size joists as the existing joists and cantilever them 2’ to gain the 24” you’re requiring. I’d install solid blocking between the new cantilevered joists and clip each joist to the top of the new beam with a Simpson A35. I’d use Simpson “U” Series for the connection to the 3-sistered joists. 

Then, I’d reinstall the diagonal bracing. 

Extend existing deck covering as required.