As described this isn't possible that I am aware of. Check out the response from @Phil_Vallender on this post.
As he mentions, it's not really 50/50 or even because it's dependent upon availability. If you want a perfect split you can rotate leads evenly using a workflow first and then allowing them to book a meeting based on the owner of the contact.
Hope this helps!
Josh
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Josh Curcio HubSpot support and inbound marketing for OEMs, contract manufacturers, and industrial suppliers. HubSpot Platinum Partner & HubSpot Certified Trainer