Would the neighbors be open to some kind of joint venture agreement?

Open to joint ventures and all that good stuff. 

. - doesn’t require a level floor so no bouncy boards or squeaky flooring joints. - so easy to clean as there are no seams for gunk or smells to work into.

Should I try to find a new bank that can do a joint account?

I have properties we could joint venture on.

Use a high end click lvt and glue butt joints together with g-2 loctite.

Is the only way to put the money in a joint account?

You could also form a joint LLC that is owned by her and your LLC 50/50.

However, if the vendor is still personally on title as a tenant-in-common, there may not be a mortgage registered ... in which case, a conventional lender may not see the property at all ... or will simply see a property you own jointly with a another party.That said, you will still be signing an agreement with the conventional lender in which you state that you have disclosed all such debt obligations :-)

I don't really have time to get multiple quotes since this needs to be fixed ASAP (tenant currently cannot shower as it is backed up).He claims that putting "copper sulfite at the joints" will "eliminate any risk of roots growing around the new piping."