Which is better: to seek employment to help the mother and relieve her of the hardship of work, without guaranteeing the performance of prayers in congregation, or to start a private project that allows for maintaining congregational prayers but delays helping the family?

It appears that what is preferable is to engage in work that brings benefit to the mother, her comfort, and the family's advantage, while striving to maintain congregational prayer in the mosque as much as possible. If that is not feasible, then pray in congregation at the workplace. If going to the mosque would result in losing the job or the manager preventing it, then you are excused from attending congregational prayer.