If the servicemember is not obligated on the loan directly by signature or "indirectly" by virtue of a community property state, I'd say no, it is not a covered loan and 6% wouldn't apply.
You may still have issues if she claims she was materially effected by his being called to active duty. The spirit and intent of the SCRA are still there. But I believe the requirements do not exist for coverage. If you want to evict or foreclose, it gets muddier as dependants have some protections here. But it doesn't sound as though they lived there or provided support for the dad who may be there. The SM is pretty much apart from all this, as is the spouse.
I think you may be in a position to shore yourself up and take actions to cure the default, but I'd recommend using counsel. And be sure they and your bank's management know the SCRA issues. You want to be prepared.
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AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell