Can I use Bitdefender's antivirus and antimalware software at the same time?
I think there's a misunderstanding here. Viruses are a type of malware. Most modern 'antivirus' solutions are more correctly described as 'antimalware' since they also stop non-virus forms of malware.
Total Security is Antivirus Plus with additional features. Namely, apps for Mac, Android, and iOS. Also has two additional device licenses to help cover the additional devices. That's it.
I don't usually recommend paid antimalware solutions unless there is a specific feature you will actually use. I personally use the free version of Bitdefender right now, although Kaspersky is my other common recommendation.