Sniffer & Wifi

Hello,
I am no guru when it comes to sniifers so I need some guidance. I want to run a sniffer (Wireshak! or else) on my PC (LAN Ethernet) or laptop (Wifi 802.11b/g) to capture/sniff all data on my home network. I have D-Link WRT110 router with WPA2, with some laptops and smartphones connected to it. I want to check what my kids are doing, the web sites they visit, the chat rooms and even reading the chat history (like Whatsapp on smartphones).

Is that possible to do with Wireshark or I need something else? If possible:
- What version of Wireshark do I need?
- Once installed, what parameters do I need to set?
- Once captured, do I need to decrypt the datd and if yes, how?

I'd like to read responses on this. I dabbled with it and never understood how to get it to work and read/ interpret the sniffed packets.

Any help here?
I am particularly interested in looking at WhatsApp chats on Blackberry. I
know there are certain whatsapp chats being deleted and I won wondering:

- Is there a way to auto backup or auto save WhatApp chats on their device which can be retrieved after they delete the chats?
I have access the the phone and can install whatever app I need

-How can intercep or sniffer Whatsapp on Blackberry using Wifi?