Should a young man propose to the sister of a girl he was previously engaged to, especially if he desires to propose to the girl herself?

It is not advisable to attend the engagement party for reasons including the renewal of the relationship with the female colleague, and because such parties often involve forbidden acts, such as the suitor putting the engagement ring on the fiancée before the marriage contract and seeing her in her full adornment. One can apologize in a suitable manner. As for the questioner's relationship with the female colleague, if it is upright and he desires to marry her, he should propose to her family; otherwise, he should cut off the relationship with her.