Not sure what you mean by "the problem is if I delete something"? That is, what do you want to happen in respect of deletions? By default, a SmartSync profile will replicate a deletion to 'the other side' (in either direction), but you can tell it not to instead. Or, you can let it do so, but also use Versioning to keep a hidden copy of the deleted file (on the side where Pro deletes it, not on the side where you did), which you can manually retrieve if you want.
Basically, once you have a common folder on the NAS and have replaced your docs & pics content on the PCs, set up a SmartSync profile on each PC for each folder branch on that PC <> the corresponding folder on the NAS
Bear in mind that you need (for a schema with an interim repository) three processes (per branch) to be run to replicate all files in each direction, thus
PC1 <> NAS
PC2 <> NAS
PC1 <> NAS
If you omit the last step, changes on PC2 will not make it to PC1 (on that occasion) - they will only make it as far as the NAS. You should try to ensure no files are changed during the above session, or some of them may 'lag' until the next session. For example, if you change a file on PC1 during stage-2 above, it will stay there until stage-3, at which point it should transfer to the NAS OK but it will not get to PC2...
Basically, once you have a common folder on the NAS and have replaced your docs & pics content on the PCs, set up a SmartSync profile on each PC for each folder branch on that PC <> the corresponding folder on the NAS
Bear in mind that you need (for a schema with an interim repository) three processes (per branch) to be run to replicate all files in each direction, thus
PC1 <> NAS
PC2 <> NAS
PC1 <> NAS
If you omit the last step, changes on PC2 will not make it to PC1 (on that occasion) - they will only make it as far as the NAS. You should try to ensure no files are changed during the above session, or some of them may 'lag' until the next session. For example, if you change a file on PC1 during stage-2 above, it will stay there until stage-3, at which point it should transfer to the NAS OK but it will not get to PC2...