Earlier quoted context omitted.
Are they actually underwater or do they just have higher loan payments than rental income? If it's the latter, let them sell some properties or transfer them to the bank in lieu of loan payments.
Who says those properties are worth their book value? This is how a crash happens these days - distressed asset holders forced into fire sales of the assets themselves, lowering asset values and putting more of the holders into distress.
Another alternative is for the real estate trust to sell new shares into the market and use the money to pay the bank, or pay the bank in new shares. That dilutes the existing shareholders but doesn't force a fire sale of the properties.