Take your checkbook and a contract, you can feel the tension leave the room when they sign.Lawyers, agents, brother in laws, etc. will all kill a real deal.

What steps should I take to ensure that if our business deal somehow goes bad, it doesn't create personal tension in the family?

The source of the fear takes the form of a incessant voice in the head and/or physical discomfort (itching,unnecessary movement, tension, short of breath, rapid heart beat, etc.)

What would be good ways to ease the tension here?

The house may not show well and if the current tenant is there during the showing there will be tension or worse.

Depends on alot of factors, but - ultimately both of you have to be satisfied with the deal, otherwies the aggravation, tension and recriminations will never be worth the profit.

However, I would try to work out a solution with the other landlord before doing this, as it could create some unnecessary tension if you didn't.These are just a few ideas off the top of my head.

The next step in the slab process is installing the post-tension cables and vapor barrier.

I think tension only builds when the rules are unclear/inconsistent.Good luck!

This will reduce any tension between you and the tenants as it is not your fault that the owners said NO to an improvement.