Cure is in Red Bottle.
The bottle red contains label saying "At least two of these bottles were made by Menes"
This statement either can be true or false.
If the statement is True then that bottle was made by Nil
Then other two bottles were made by Menes.
Because Menes is always telling lies both labels in bottle yellow and blue are false. Then both of those bottles contains poison and the remaining bottle Red contains the cure.
Lets assume the bottle red was made by Menes. Then the statement on the bottle also false. Then Menses has created only one bottle and which is the bottle red.
In that case remaining bottles Yellow and Blu bottles were made by Nil. Then statements on those bottles should be right. Both yellow and Blue bottles says it is the cure which should be correct but our initial condition "Two of the bottles contain deadly diseases" will not fulfill.
Therefore the statement on bottle Red should be correct and it wad made by Nil. Since Menes has put false statements on Bottle Yellow and Blue They were poisons and Bottle Red contains cure.