Although the Jalapeno seeds make the Jalapeno peppers hotter they are still very hot even without the seeds.
In a Jalapeno pepper the seeds are not what really makes the hot pepper hot but instead it's the capsaicin which is contained inside the Jalapeno Pepper itself.
The seeds are coated with some of the capsaicin as well but the seeds aren't what makes them hot so even when you remove the seeds from Jalapeno Peppers the peppers are still hot.
If you want peppers that are not hot then you need to get some bell peppers but all Jalapeno peppers will remain hot even without the seeds.
In a Jalapeno Pepper the hottest part of the Jalapeno Pepper is the placental material surrounding the seeds so if you want to remove some of the heat from the pepper you'll need to remove the placental material.