If you are in the US you can only watch these seasons of Terrace house on Netflix US:
Terrace House: Boys & Girls in the City (2015-2016)
Terrace House: Aloha State (2016-2017)
Terrace House: Opening New Doors (2017–2019)
Terrace House: Tokyo 2019-2020 (not all episodes)
You will need a Japanese VPN in order to watch:
Terrace House: Boys & Girls Next Door (2012-2014)
the newest episodes of Tokyo 2019-2020
The cheapest VPN I found is called Windscribe (https://windscribe.com/upgrade?affid=nr0kqld5) and will cost you $2 a month for unlimited bandwidth. Most other reliable VPNs will cost you around $10 a month. I haven't been able to find a free VPN that works reliably. If you know of one please leave a comment below!
When signing up for Windscribe make sure you choose "Build a Plan" since it is the cheapest option. Windscribe charges $1/month for every VPN location you choose with a $2/month minimum. So you can either choose 2 locations or add unlimited bandwidth for $1/month which is what I did.
Make sure you select at least "Windflix JP" for your locations since that is the Japanese VPN location that will allow you to watch Terrace House.
Terrace House 2019-2020 will already have English subtitles but if you want to watch Boys & Girls Next Door you will need to load subtitle files which you can find for free on Reddit here: https://www.reddit.com/r/terracehouse/comments/6jh6cx/terrace_house_boys_x_girls_next_door_week_1/