Unfortunately I cannot speak to any remote possible or imaginable source outside of the Bible that may speak on the topics you mention. You seem to say that others have said this. Can you provide any evidence that is being used by the others to make these claims? Otherwise, this sounds like an unfounded statement without any evidence so there is little need to trust or believe it.
The Bible is my primary source for understanding Jesus, and I would be concerned if the stories about Him were inconsistent. However, I find that they are consistent, so I do not have any alarm. The Bible does give an example of when people during Jesus’ day claimed that He was working with the devil:
Matthew 12:22-30 NASB
 Then a demon-possessed man who was blind and mute was brought to Jesus, and He healed him, so that the mute man spoke and saw.  All the crowds were amazed, and were saying, “This man cannot be the Son of David, can he?”  But when the Pharisees heard this, they said, “This man casts out demons only by Beelzebul the ruler of the demons.”  And knowing their thoughts Jesus said to them, "Any kingdom divided against itself is laid waste; and any city or house divided against itself will not stand.  If Satan casts out Satan, he is divided against himself; how then will his kingdom stand?  If I by Beelzebul cast out demons, by whom do your sons cast them out? For this reason they will be your judges.  But if I cast out demons by the Spirit of God, then the kingdom of God has come upon you.  Or how can anyone enter the strong man’s house and carry off his property, unless he first binds the strong man? And then he will plunder his house.  He who is not with Me is against Me; and he who does not gather with Me scatters.
So the answers I would give are the same as Jesus Himself gave. If He cast out so many demons while working for demons or being a demon, how can the devil be working against himself? It does not make much sense.
Please give this some thought and let me know if you have any clarifying points why someone would say the things your purport that they claim.
I pray for clarity and blessings on your search!