I would get a domain name and use ddns to update your rotating IP. Then I would setup wireguard VPN in split tunnel and have your parents network tunnel back to your piholes for dns resolution.
I use cloudflare API for ddns updates but there are plenty of choices for that. If you're using cloudflare for DNS just keep in mind you can't proxy the DNS entry for the ip for your VPN host as CF only forwards traffic over certain ports and they are not configurable (on free plan anyway not sure about paid).