Why are the tires on a Ford freestar leaning in on top

Leaning in would be excessive camber. Some slight leaning would be normal. I would to the vehicle to an alignment shop and have them look at it. You may have some worn suspension parts or it may just need an alignment. An alignment requires special equipment and is not a do it yourself type job. Plan on spending somewhere around $100 plus or minus for just a 4 wheel alignment. Replacing damaged or worn parts would be extra. Also excessive tire wear can be caused by the alignment being off, so pay for alignment now or pay for tires later.