If you delete photos from the ipad, will they still be on my other devices?

Depends.

If you are using iCloud Photos then all changes including deletions are synced across devices using the same Apple ID for iCloud, so deleting images from one device will delete them on all devices.

If you are not using iCloud Photos, then no. Photos one each device are independent of photos on other devices.

Not if you have iCloud Photos turned on in all of the devices.

iCloud Photos is a syncing service. Any photo you delete from a device where iCloud Photos is turned on will also be deleted from iCloud and from any other device connected to iCloud Photos. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See the following Apple article for more information: Set up and use iCloud Photos - Apple Support