I would suggest having your elderly family member finding the comfortable seat height in the drivers seat. When you arrive at that perfect height, match the passenger seat with that using the seat jacks you mentioned.I had no idea raising the car voids the warranty...I think I will order the seat jackers tomorrow. The company is called Desert Does It out of Utah. I don't like tampering with seats, which could be safety issue, but I'll buy it and take it to my mechanic. I'll go from there...I'll let you know. I just need that seat raised an inch or two. Thank you for helping me and your support!