Every sitter on Rover is independent and may have different ways they perform the house-sitting service. Also, each sitter sets his/her own rates and may discount for additional dogs, but may not. This is why it is important to read each sitter's profile carefully and then discuss your needs and how they will fulfill them.
A drop-in is quite clear. The sitter comes to your home for a 30-minute visit. The sitter will spend time with your pet and will, at a minimum let them out. Some may do a walk; others may not.
However, house-sitting services vary widely. According to Rover, each "night" is good for up to 24 hours of pet care, which would include feeding, walking, playing, etc. It should be considered a premium service, costing more, because the sitter is staying in your home (although not necessarily 24/7) but may go out to take care of other pets in his/her care. There will also be "additional pet" charges for this service.
https://support.rover.com/hc/en-us/ar...
Not all sitters do this. Some may only stay overnight (e.g., 8pm-8am) and then you would need to also book a drop-in for mid-day or similar.
The "let out every 2-3 hours" is only a guideline that this sitter is there to ensure your pet has access to potty breaks as needed. I know it is quite confusing, but decide on exactly what you need and then talk to several sitters offering house-sitting to find one that meets your pets' needs at the right cost.