Hi
Its likely that the Lync clients that have sfb emoticons will probably mean they have the April 2015 patch installed that upgrades the client to sfb. The reason why they are using the lync ui will be down to your lync server / client policy.
The lync clients that aren't updated will be lync 2013 native clients. To upgrade them you first need Office 2013 service pack 1 installed, even if you only have the lync 2013 client and office 2010 for instance. Once this is installed you need this patch
installed https://support.microsoft.com/en-gb/kb/2889923
You can upgrade them all to skype ui by registry key or perferably using the client policy set-csclientpolicy -identity global -enableskypeui $true
Provided your lync servers are patched to the April 2015 CU.
thanks