Can SQL Server Management Studio Express be installed standalone? I was wondering if the SQL Server Management Studio Express (mainly for Microsoft SQL Server) be installed on a standalone machine (without any of the SQL Services and stuff) to connect to a remote database? 

I run a SQL Server 2012; I have been told by one of my managers that they wish me to create a web UI for specified users to run queries / update the database; this is within my ability of PHP; but I was thinking for ease, I could make a proposition to scrap the need for the Web UI because this will cost a lot of time for our server administrators, but install SMSE on our network machines to connect to/manage our databases? 

Is this possible? or would I have to go through the painful task of creating a WebUI which displays schemas, tables etc.
Yes, you can install Management Studio (or Management Studio Express) on a workstation that doesn't have SQL Server services. Just pick Management Tools - Complete and Management Tools - Basic during setup. You should be able to do this with any edition of SQL Server you have except for the most basic Express editions - just be aware that technically you need to possess at least one license when using it to manage production instances (though that may have loosened up over the years). 

If you don't have an edition of SQL Server that comes with client tools, or you don't have a license to use the full version of Management Studio, you can always download Management Studio Express. @Bummi recommended the RTM release of SQL Server 2012 Express, but the Service Pack 2 version is a better option - since it provides a full version of Management Studio that no longer has feature limitations or licensing requirements:


http://www.microsoft.com/en-us/download/details.aspx?id=43351


I have more thorough download/install instructions in this answer:


https://dba.stackexchange.com/a/73919/1186