Option 1 - The landlord simply sells the house on the open market. You can move or if the new owner agrees, you can continue to rent from him.
Option 2 is the simplest alternative. A landlord who wants to accommodate you.
He agrees to defer the sale of the house for 2 years or until you are in a position to get a mortgage.
You rent it at the market rent in the meantime.
He then sells the house to you at the then market price.
Option 3 You sign contracts for the sale of the house today to be completed in 2 years time. You pay a significant deposit , i.e. around 15% of the sales price. You have a right to pull out, but you forfeit your deposit.
In the meantime, he owns the house and you pay market rent.
Your option 4
This makes no sense to the landlord.
He can sell it today for €200,000
or
he can rent it for €15,000 a year for two years, and then sell it for €200,000.
You are asking for the right to buy it for €170,000 in two years time. But you won't have any obligation to buy it.
He should simply sell it today for €200,000.
Summary
The only option the landlord should consider is Option 3, but the deposit would have to be a significant figure.
It's very risky for you. If house prices rise significantly in the meantime, and you are unable to get a mortgage, then you lose your deposit.