Can you feel butt implants when you sit down?

When the buttock implants are properly placed within the muscle, you should not be able to feel them when you sit down. You should not be able to feel them at all. 

Butt implants are a great way to enhance the back side especially if you
don't have enough fat for fat transfer to the buttock a.k.a Brazilian buttock
lift. When performed properly, you should not feel your butt implant after the healing period. All of our butt implant are placed
under the muscle and looks really natural. The best way to know if you are a great candidate is to visit a Plastic Surgeon.

Yes, it is normal to feel your buttock implants when you sit, walk, or run.  Over time you will become used to the implants and will not even notice that they are there.  Apart from an augmented size, you will not be able to see the the edges of the implant or tell that they are there.  However, if you desire a more natural enhancement then you may want to consider fat graphting because you won't feel it when you sit down.