While your HP all in one should be visible to your Macs, printing from an iOS device is a different matter altogether.
Solve the first problem first: install the printer using your Mac's System Preferences > Print & Scan. Depending on your version of OS X one or more of the following will get you started:
Once you are able to use the printer and all its features from your Mac, you can configure it to share the printer and use one of at least two utilities that enable it to act as a print server for your iOS devices. There are other options as well. Get it working with your Mac first, then we can discuss your iOS options.
Thanks for confirming what I thought.
I wish to give back some additional info which might be of help to others.
The app I found allows any 'Windows' supported print/scan device to show up as an AirPrint device. I have it installed and supporting the other equipment in the house, leaving my Mac free for me.
The package is 'FingerPrint' from Collobos Software. It runs on a Microsoft platform without the need for my Mac. It's a small piece of software which iOS 6.1.4 takes very kindly to, I'm now free to take my Mac with me on travel (which I do for long projects) without having an idle printer left behind.
If I can be of any assistance, please don't hesitate to ask.