This is a consumer loan subject to all the applicable consumer regulation.
Flood applies,
ROR applies since you are taking a security interest in their current primary residence unless the second is part of the residential mortgage transaction,
ETIL would apply if the second being taken is part of the Residential Mortgage Transaction,
HMDA and RESPA may or may not apply. If you have set it up to amortize then I would say yes. If you have set it up as a single payment until the old house sells then I would say you have a bridge loan and it would be exempt,
Reg. B will apply.
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The opinions expressed are mine and they are not to be taken as legal advice.