NEW Installing Service Pack 3 for SQL Server 2014 on primary site server/secondary sites servers


I have primary site server with its DB hosted on local SQL Server Standard 2014 SP2 and two secondary sites on servers with their DBs hosted on SQL Server Express 2014 SP2 respectively. I would like to install SP3 for SQL Server 2014 on all of them so do I have to stop CM services while doing so on primary site server and secondary sites servers and is order of installing SP3 important because SQL Server upgrade for instance must be done first on secondary sites servers and only then on primary site server if I am not mistaken.

Thank you very much in advance!!!