Julia,
I think your reasoning on scenario 1 is right on. It is comment 7 that applies to this situation, not comment 5. If the property is vacant land, and they are planning to construct a dwelling, then the consumer does not yet have an interest in the dwelling, because there is no dwelling. Even if construction had begun, I think the transaction would be considered an RMT under comment 4 of the OSC to 226.2(a)(24).
On scenario #2, is your concern the early disclosures required if it's an RMT or right of rescission, or both? Based on the fact that funds are being used to purchase property B, and the loan is secured by property B, I think it meets the straight definition of RMT:
"(24) Residential mortgage transaction means a transaction in which a mortgage, ... is created ...in the consumer's principal dwelling to finance the acquisition...of that dwelling."
However, I still think the security interest taken in property A is subject to Right of Rescission, based on OSC 4 to 226.23(a)(1):
"4. Special rule for principal dwelling. Notwithstanding the general rule that consumers may have only one principal dwelling, when the consumer is acquiring or constructing a new principal dwelling, any loan subject to Regulation Z and secured by the equity in the consumer's current principal dwelling (for example, a bridge loan) is subject to the right of rescission regardless of the purpose of that loan. For example, if a consumer whose principal dwelling is currently A builds B, to be occupied by the consumer upon completion of construction, a construction loan to finance B and secured by A is subject to the right of rescission. A loan secured by both A and B is, likewise, rescindable."
_________________________
Opinions are mine and not necessarily my employer's.