Long story short I need to lag bolt a new joist in by a stairway where an old joist cracked and failed. It is one of the joists that is doubled up that ties and also acts as a hanger plate for the stair stringers. Floor is supported with a temporary assembly at the moment and is no issue. I plan to reattach new joist using 6 (3 on each side) 1/4" lag bolts about 4 1/2" long on the ends and several 3" wood screws on the face tieing to the face of the other joist. I am also using wood glue one the ends and faces when joining. The problem I'm having is on the one side there is another joist about 3" from the doubled one I need to put the 4 1/2" lag bolts into. The only way I can get the bolts in there is to drill holes in that joist and pass the bolts through it. The head of the bolts is about 1/2". Thus if I'm installing 3 bolts this is three holes on top of each other in a dimensionally 1 1/2" by 9" joist. I am not so sure this is a good idea.
I thought about just filling the holes with 1/2" dowel rod and glue after I drilled the holes but I wasn't so sure that would work. I also thought about putting a 2' scab over that section using a ripped 2x10 and lag screwing and glueing but that is alot work (wiring needs moved etc. Thoughts and suggestions would be appreciated.