You cannot share volumes between different Windows clusters. Each Windows cluster needs its own set of shared volumes.
You can add new nodes to an existing Windows cluster. It may be possible to mix 32-bit and 64-bit nodes on the same cluster, but I have not tried it. However, if this is successful, you should then be able to install SQL 64-bit on your new nodes. If this works, then you can fail over from the 32-bit node to the 64-bit node and evict the 32-bit node from the cluster. Ultimately you will have a cluster using only 64-bit nodes that can access all the memory on those nodes.
If you are running SQL 2012 RTM or below, all the nodes in the cluster must use the same operating system. With SQL 2012 SP1 and above, you can add a Windows 2012 node to a Windows 2008 R2 cluster, and ultimately migrate the cluster to Windows 2012.
Original author: SQL Server FineBuild 1-click install and best practice configuration of SQL Server 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005. 1 Dec 2016
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