Is there a difference between Bantu and tolong?
bantu = tolong = to help.
They are synonyms according to KBBI, but sometimes "tolong" is translated into English as "please", like this:
"Tolong bantu saya" = Please help me.
In such a sentence, you cannot switch those two words, so although they're synonyms according to KBBI, the words can be used differently.
And can both tolong and mohon be used for "please" in all cases?
No, not really.
"tolong" = to help.
"mohon" = to ask politely.
Depending on context, these words are translated into English as "please".
"silakan" = please.
"silakan" is actually a polite command.
"silakan" is used to ask/invite/encourage someone to do something, like this :
Silakan masuk = Please come in
Silakan makan = Please eat
Silakan minum = Please drink