Before deciding whether your loan can be called under a due on sale clause, you or your attorney might want to review 12 CFR 591 which I believe may provide in part:
§ 591.1 Authority, purpose, and scope.
(b) Purpose and scope. The purpose of this permanent preemption of state prohibitions on the exercise of due-on-sale clauses by all lenders, whether federally or state-chartered, is to reaffirm the authority of Federal savings associations to enforce due-on-sale clauses, and to confer on other lenders generally comparable authority with respect to the exercise of such clauses. This part applies to all real property loans, and all lenders making such loans, as those terms are defined in § 591.2 of this part.
§ 591.2 Definitions.
For the purposes of this part, the following definitions apply:
(b) Due-on-sale clause means a contract provision which authorizes the lender, at its option, to declare immediately due and payable sums secured by the lender's security instrument upon a sale of transfer of all or any part of the real property securing the loan without the lender's prior written consent. For purposes of this definition, a sale or transfer means the conveyance of real property of any right, title or interest therein, whether legal or equitable, whether voluntary or involuntary, by outright sale, deed, installment sale contract, land contract, contract for deed, leasehold interest with a term greater than three years, lease-option contract or any other method of conveyance of real property interests.
§ 591.3 Loans originated by Federal savings associations.
(a) With regard to any real property loan originated or to be originated by a Federal savings association, as a matter of contract between it and the borrower, a Federal savings association continues to have the power to include a due-on-sale clause in its loan instrument.
(b) Except as otherwise provided in § 591.5 of this part with respect to any such loan made on the security of a home occupied or to be occupied by the borrower, exercise by any lender of a due-on-sale clause in a loan originated by a Federal savings association shall be exclusively governed by the terms of the loan contract, and all rights and remedies of the lender and borrower shall at all times be fixed and governed by that contract.
§ 591.4 Loans originated by lenders other than Federal savings associations.
(a) With regard to any real property loan originated by a lender other than a Federal savings association, as a matter of contract between it and the borrower, the lender has the power to include a due on sale clause in its loan instrument.
(b) Except as otherwise provided in paragraph (c) of this section and § 591.5 of this part, the exercise of due-on-sale clauses in loans originated by lenders other than Federal savings associations shall be governed exclusively by the terms of the loan contract, and all rights and remedies of the lender and the borrower shall be fixed and governed by that contract.
While I agree a lender foreclosing because of the due on sale I'm not sure it can't happen.
In addition, assuming you received an Owner's Title Insurance policy when you purchased the properties, if you're going to convey the property to an LLC, make sure the Grantee meets the definition of Insured under the policy. If it does not it probably will not be considered an Insured under the policy.