Buying out a Partner

[Thomas Smith]

I am in a partnership in which we currently own 11 units together.  A couple single family and a few multifamily.  I put myself into the unfortunate position of being in a partnership that is 95% me and 5% the other guy in terms of workload (we are both 50/50 financially).  We have only owned our properties for a couple of years.  Luckily we purchased them all well below market.  So my idea to end the partnership but preserve a friendship was to list our properties.  This way we both make a little cash and the friendship remains in tack.  Unfortunately, his dad is the realtor and this is his part-time gig.  So you can see how effective this has been.  

Yesterday, my business partner asked me to buy him out.  However, his buyout number was well above the amount we would get even if we sold the properties today (since we still have mortgages to pay off first).  

There are a few of the properties that I would love to still own but now that I know his "buyout" number, there doesn't seem to be a way to pay him off and keep the properties (he's a bit inflated with his thinking).  Does anyone have any suggestions for handling this situation?  How should I determine a buyout number considering we are very early into our mortgages?