I have a dark hallway which although there is a ceiling light Id like to add two wall sconces (already purchased)... what is the best way to do it? Id like to connect them to the ceiling light so that they all can share the same switch...

Depending on the Location, you can connect to the existing light, separately, or Existing light, to new light, then from first new light to second light, If you have a neutral and switchleg in switch box, you can run from their, whichever is least destructive, easiest, and cheapest if possible.
Is this on 3 ways(2 switches controlling the light)

You could also run a swag from both lights to the old ceiling box. It would not look very nice but its works. Othjer option is to open the walls in certain spots to pull cable.

What is above hallway? If u have an attic above, u can run the cables for the sconces with no damage to walls or ceiling.

Cut opening in wall for box u will use for sconce. Drill 3/4 inch hole in wall plate that lines u up in the bay u made holes.

Turn off electric to ceiling light. Run two cables from ceiling light. One cable to each opening. Hook black and white wires to wires that are hook to light. Hook ground to existing ground wires.

Install cable into each box and mount in opening. Hook wires from sconce to wires in box. Don't forget ground wire. Mount sconces on boxes and turn on electric.

Good luck

Chuck