Outdoor direction antenna is the old way to do this. You buy complete outdoor bridges for the same price. Pretty much they put the electronics inside the antenna so no more worries about expensive microwave cable and having to buy equipment with external antenna connectors.
Look at ubiquiti airgrid. I have gone well over 1000ft with one on each end they say they go 20km...not that I believe that. These are about $75 each but are large grid antenna. Engenius sells small flat box type units that don't go as far but would meet your needs.
There should be no IP conflicts.
If we look at a simple design you would cable a AP in your place to your parents router with ethernet cable. There still is only 1 router (if you use a...