Assalam o Alikum,
الجواب وبالله التوفيق
The requirements which have been specified in the light of the Shar‘ai teachings and have been rendered mandatory, the guidance which has been given and the advice provided regarding the correctness of this procedure (i.e.in regards to financing houses through murabahah)by the respected ulamah kiram of Shariah Board of America to Devon bank, if all of those conditions are implemented with complete and necessary details, then from a Shar‘ai standpoint this method will be considered correct. There is no inclusion of riba in it nor is anyone involved in interest.
The procedure of Islamic financing through Islamic murabahah compared to the banks following the classic capitalism at their core have fundamental differences and based on these fundamental differences one is considered halal whereas the other haram, one is rendered permissible where as other impermissible.
It is evident from your question that you have ishkal(difficulty) regarding your loan transaction with the bank i.e. whether the loan taken or the transaction performed with the bank in a halal manner is involved in a mix of interest and non-interest based business.
There is no doubt regarding the fact that banks are in general involved in interest based transactions, however, just this fact does not render performing loan transitions with them, as impermissible. This is because in the light of fatawah keeping relations and dealings with individuals who have a mixed income (i.e. from both halal and haram sources) is permissible in the case when the majority of their income is from halal sources. The general deposits stored at the banks have a major share which is from halal sources where haram compared to the halal amounts is usually lesser. This is because the moneys deposited in the banks are of different categories:
From the above areas, only 4 and 6 pertain to sources which are considered haram and impermissible for use in the light of the exalted Islamic Shari‘ah. The remaining sources cannot be considered as absolute haram. Instead, the more probable view is that moneys deposited through the other sources is halal. When their major share has been established as halal, then in the light of the Shar‘ai ruling, there is no two ways in the gunjaish(i.e. provision of permissibility) to perform transaction with them. However, if someone has taken the commendable step of leaping forward and following the path of taqwa then that individual is definitely worthy of praise and appreciation. Such and individual will receive the reward for refraining from mushtabihat however in the light of taqwa and wara‘ the fatwa will not be changed.
واللہ اعلم بالصواب