Both of us are ready, but how do we motivate/entice the other property owner to sell?

If the owner is willing to let you have the place subject to the existing mortgage, paying some portion of the $18,000 the owner is out ($55K less $37K) might entice the owner to give you the keys and quitclaim you the property.      

I am doing 2 conventional deals right now, so having the HML would be enticing to conserve for other deals I am considering.Much appreciated in advance!

Having $100k to potentially write cash offers and get some great deals is very enticing.

Yes, screening comes into play, aside from all of those obvious operational points not mentioned you will have a lot better time enticing a horse to come your way with an apple in hand than a fist full of nails. 

It is enticing to take your available cash and make down payments on 4 or 5 rental houses in Alabama (as opposed to one in SoCal) in order to spread your risk, but that is illusory.

In This instance it might make sense to offer a flat dollar amount for a six month loan or something similar to entice someone  Almost anyone who approaches you online about private money is a scammer so be diligent! 

I would recommend leveraging your knowledge and hustle to entice someone to partner with you on a deal.

The idea of buying and holding real estate to provide both an immediate revenue stream and a long term investment is very enticing. 

Lastly, if this is the first deal you might want to think about offering a greater ROI to your partner to entice him/her to invest.