I finally had a good jump!
After about 10 jumps where the chute didn't open properly, I re-strung the chute according to what I learned here:
This time, the chute opened and inflated. I think I need to bring the front of the chute down a little, though, because the chute collapsed a little every time my dad tried to steer it (I flew the plane).
On the next jump, the chute didn't open and he landed about 40' up in a tree. Shortly after that, my dad flew his paraglider into a different tree, again about 40' up. I went home and got my bow and and arrow with a golf ball on the tip. I shot a string over the chutes and pulled them down with only minor damage.