Can u delete photos on ur iPad to free up space and still keep them on ur computer and iPhone?

Not if the three devices (iPad, iPhone, and Mac) are all connected to iCloud Photos with the same Apple ID. Deleting a photo from any one device deletes it from iCloud and then from the other devices, just as additions and edits are propagated among the devices.

If you need to reduce the space that photos take up on your iPad, look into the "Optimize iPad Storage" option.