Not sure what you mean ... as in model
seats into the vehicle ?
Use O2, and you can make a seat out of 2 boxes. 1 Box is the back of the seat, 1 for the seat itself.
A seat with head-rest. thats 3 boxes
...... or, copy (Control-C) the seats in a BIS model, open your model .... paste.
Move it around until its in the right position.
The path to the textures should be presevered.
Beware but, by community rules, using BIS 3D material means your raw model is now public domain, its requestable to be handed over.