If you don't need Navigation system, you can go for a 2015 new RX350 within
your
budget. However, you have three children. It's better for you to have a
third row if your children are still under 10 since you mentioned that your
parents visit you sometimes.
If you need navigation, you can go for a 2014 certified pre-owned RX350 with
less than 2k miles. The price should be around $4k. Remember: go for the
CPO and go for a dealership with good reputation.
Have a nice weekend.