Are these sentences correct:
1-He is always early with the rent.
2-He is always beforehand with the rent.
3-He is always late with the rent.
4-He is always behindhand with the rent.
One and three are correct.
It would be ok to say that "He is behind in the rent."
Which does not refer to the timing of his payments rather his overall payment history. Ex: He is three months behind in rent.
Also, "behindhand" is not a word.