HOWI CAN I INSTALL SKYPE IN MY iPad 2(16GB)?

Internet search " International calling codes - Nations online project".

Why do you need Skype since you have FaceTime?

Reinstall skype.

Use Safari and go to www.skype.com. From there hit sign in. There are two links- one for "I forgot my password" and one for "I forgot my username". Use these to figure them out and then enter them into the app once you have them again.

Download the Skype App from the App Store and log in using your Skype ID

Making video call iPad. This may be helpful.
Do you have a profile picture set up?
Are they able to see you at all during the call?
Which iPad do you have?

You don't have to delete his account. It is simply the "default." If you setup your own mail account, you can then make your account the default. You will afterwards set up your own Skype account using your own email address. Nothing stops you from setting up a Gmail (Google) account. If you don't know how, simply google "how to set up a google email account." As to how to make that the default account on your iPad, where the menu item is to do that may depend upon the version of the operating system. Here is one depicted instruction set:

How do change my default Mail account on iOS 10 or you might find the following of use:

How to Set up Email on an iPad

There are a few apps that allow mobile calling, such as Skype, but you'd need WiFi or 3g + Skype minutes.

If you want to install them directly you can do so here: http://ipad-os.net/how-to-install-ipa-directly/

For video guides on using the iPad head over the http://www.tabletmastered.com/blog/

I don't know about Yahoo messenger, but you can certainly download Skype onto your iPad. Search for 'Skype' in the App Store, and you'll be able to download it free. There is no iPad specific version of Skype, but the iPhone one runs and works fine.
As for Yahoo messenger - do the same thing, run a search in the App Store to see if you can get it for iPad. If not, see if you can do it via the web - Safari on iPad is a very capable browser, much more so than Internet Explorer, at least.
Hope that helps!