I agree with this completely.
Also when the truth comes out it will be a total shit show and your husband and yourself whom knew what was going on, kept something so serious from his wife, WILL be vilified.
It will be so convenient to scattergun the blame and you two will be a great focus for her upset.
You will be very harshly judged for facilitating him getting in deeper financial trouble.
They have children and neither of you are thinking of them.
Your husband is actually thinking of himself and how he wants to be seen by his friend.
He is not doing the right and honourable thing by helpung this friend lie, and dupe his wife futher.
Your husband hasn't thought this through.
If I were you I would email your husband your long list of reservations and concerns and lay it all out what is likely to happen and how he potentially is involving your family in a very ugly public situation.
Your names will be mud in all of this.
How would YOU feel if your husband did this to you?
If I heard that close friends had kept shit like this from a wife, I would be appalled.
YOU are now fully involved.
25k is a short term plaster.
This reeks of the desperation of some sort of gambling.