Yes. Any group call can have the host plus up to 25 participants, and these can be either people using Skype or calling in on a mobile or landline.
However, if you are using a version of Skype for Windows desktop older than 3.8, you can only host up to 4 participants.
Download the latest version of Skype.
Each call will be charged separately and each call will appear on your account as a separate call. If you have less than 1 minute of Skype Credit remaining during the group call, then this call will terminate unless you have a means of adding more Skype Credit when requested. Other calls will continue until they have less than one minute of Skype Credit left.
There is no additional charge for calling mobiles or landlines during a group call - you simply pay for the time used, for each call.