what happens to solidify the family during their migration? what is ma's philosophy of "holdin on"?

Many things happen that bring the family closer. Grandpa dies as does grandma a short time later. They near starve at some of the the camps that they work at.Still Ma Joad insists on "holding on". The family is what keeps the Joads going and Ma demands that they stick together. She is even weary of Tom running away for breaking his parole and being involved in the altercation that killed Casey.