I want to say that their manners crumbled form the very beginning because their manners were unsteady or shakySomething that is built on shaky foundations is likely to collapse.
Are you saying that their manners likely to collapse, in the sense that their current attitude to good manners may suddenly crumble, to be replaced by good manners?
This means that "morality" works well in place of "manners"? Is it correct to say the "the basis of morality was shaky"?Hello Huda
There's a major vocabulary problem here.
'Manners' means behaving politely in society and has nothing to do with morals. Some of the most vicious criminals are very charming and have excellent manners.
So we need to find other expressions for what these people are lacking. The shaky foundation expression can certainly be used.