This post is almost a year old but, I solved this without third party services. Maybe I just want to show off.
If you have 2 accounts,
1. Creat account, set name and photos which can use in both accounts.
2. Invite co-host (the one created in 1) from all the listings and accounts.
3. Accept co-host proposal from account you created in 1.
Make sure you set the fee 0% to co-host. You can invite co-host from your listing managing page, tub of bottom.
That's is. Then you can see all the listings from 1 account. No need to switch accounts.
Best thing for me was getting notification from every accounts via Airbnb apps.
And co-host can do all the jobs you need in daily basis. You can see details from this airbnb help page.
https://www.airbnb.com/help/article/1534/what-can-a-co-host-do
Hope this will help some of people who isn't familer with co-host system.