Enable UAC on both systems
Win 7 - ESS + Adguard should be enough and use MBAM Pro as an on demand scanner
Win 8.1 - KIS is enough and use HerdProtect as an on demand scanner
Very nice configuration, upon downloading samples its better to test on separate computer (not your production system) or use fully virtualized/partial like Sandboxie and Shadow Defender or virtual machine if enough computer specifications.