Sharing Hotspot from the mac that the iPhone or iPad can connect with?
You can create a Personal Network from the AirPort (Wi-Fi) menu.


Select Create Network ...
Define a name for your Network
Select the channel
Select the security (if selected, define a passphrase/key)
Click Create.




In my case I also have to define the IP addresses on the devices.

On your MacBook:


Go to System Preferences
Network
Select the Wi-Fi connection
Click Advanced
Select the tab TCP/IP
In the first field select the voice Manually
Set an IP (e.g. 192.168.1.1)
Set a Subnet Mask (255.255.255.0)
Click OK


On the iOS devices:


Go to Settings
Wi-Fi
Click the blue arrow on the righ of your ad hoc Wi-Fi connection
Select the tab Static
Set an IP (e.g. 192.168.1.2)
Set a Subnet Mask (255.255.255.0)