Why not just tell the couple “I completely understand that you want a mortgage now. However, I’m not a bank. I can help arrange a meeting with your local mortgage banker if you’d like…”
A little bit of sarcasm with your overly-demanding, spoiled-sounding rich kids is in order here…
Enough blaming their attitudes on anyone but them & start taking action to represent what your values & true feelings are.
There is simply no room for such Chutzpa on their end here.
And if this does mean a strained relationship with your kids — if this isn’t the straw that breaks the camel’s back, something is bound to soon. Because they’ll just become more & more demanding.