The better question might be why are you getting viruses with such regularity that this is a concern?
Photography
A place to politely discuss the tools, technique and culture of photography.
This is not a good place to simply share cool photos/videos or promote your own work and projects, but rather a place to discuss photography as an art and post things that would be of interest to other photographers.
I am not getting viruses. It's a precaution the same as why it is recommended to get a drive offsite: An unlikely event such as fire or theft etc. Just trying to do it right.
you're overthinking it but if it bothers you, turn on the synology antivirus module
You need a version history or time stamped backups going back far enough that preceeds the issue.
Depends what you mean by Infection, the main thing you want to protect yourself against is Ransomware vulnerabilities which is the biggest issue i see with Synology/QNAP/DROBO etc... I make good $ with clients that get infected. My recommendation.. get yourself a NAS such as a Synology, and backup to the cloud, there are many cloud providers which support NAS backups, Synology has their own service and its very affordable. Onedrive is also a very good alternative as you mentioned, however the limitation is 1TB, remember the "infection" will not be transferred to Onedrive, assuming you're concerned about viruses, just get yourself a good AV such as Sophos or Bitdefender and update your OS every month. From what i read, you're safer backing up to a proper cloud provider than storing another NAS at your parent's house... a cloud backup can be encrypted so that no one can access those files... Encryption + MFA and you're relatively safe.