I tried to sync for several years and it never worked. I tried everything. Eventually we just moved to using one computer and sharing it. Its not healthy to spend all the time on it anyway. Having a pooled machine has a number of social benefits as well.
So we have a single laptop, three smartphones (my oldest daughter has one as well) and they're all handed in weekly to me for data extraction and archival.
The laptop is a Lenovo X201 so it can go anywhere and we have a docking station and full desktop setup if you need anything a little more healthy to use.
Yes. I had one. It died suddenly and left me with a £400 bill for a new one. Fortunately I backed up the NAS to an external disk but from this and other experiences, I've come to a general rule:
the reliability of a backup system is inversely proportional to the number of moving parts
Hence why I use beyond compare to manually sync files to two physical mediums from the master copy on my laptop. One encrypted USB stick I carry on me at all times and one hard disk that lives in a fire safe.
So we have a single laptop, three smartphones (my oldest daughter has one as well) and they're all handed in weekly to me for data extraction and archival.
The laptop is a Lenovo X201 so it can go anywhere and we have a docking station and full desktop setup if you need anything a little more healthy to use.