Not sure if there will be compatibility issues by my recommendation is either stick to Avira or MSE as RT protection.
Unless OP means Windows Defender as opposed to MSE.
Pairing MSE with AVIRA will not bring you anything extra to the table apart from some more RAM and services usage.
On On-Demand scanners, MBAM is more than enough. If you wish to have a second opinion scanner, add Hitman Pro (scanner only which is free) and ditch SAS since it is not what it used to be and what SAS detects, MBAM is sure to detect and has better removal capabilities.
Finally, consider adding a backup solution free:
*Built in windows 7 backup solution, which will allow you to mount the VHD as an actual drive to retrieve specific folders/files or restore completely the backup;
*Paragon Backup and Recovery Free (2nd option I recommend if the user does not wishes to use the windows 7 solution)
*EaseUS Todo Backup Free
*Macrium Reflect Free