You can make any abilities stack with each other by changing the buff of the other ability. Example, Brilliance Aura 1 has the buff Devotion Aura which increases mana regen by 5, and the other one, Brilliance Aura 2 has the buff Vampiric Aura which increases mana regen by 5. If you make the 2 heroes close to each other with different buff and with the same ability, it will stack.
Here's the proof: