The kitchen should be vented directly above the actual vent so that the fumes, grease etc goes straight up and out the roof. This is why a plumb bob is used. Kitchen fumes and stuff don't like to make turns and actually won't, they will collect on the up side of the turn and just lodge there and cause blocked pipes.
Vent the kitchen up and out of the roof. Venting kitchen into the attic is a no no.
Bathroom could be vented in the attic IF you have good and adequate venting. Other wise it should be done as the kitchen. Also, it does not like to make turns.
Look at dryer venting pipes. if there is a turn in the hose the lint will collect on the turn and start creating a blockage and therefore ruin your dryer and a possible fire area.