Hi there Nina and thanks for this question.
It is no surprise your cats are intimidated by him, as he is a Tom who may be territorial and eager to mate, even though they are neutered.
Toms are much more likely to try and mate with cats, but also to fight with them.
If he is regularly in that same area, he has likely claimed it as his own.
If your local rescue or charity group can check him over and neuter him, that would be great. They should then re-home him in a suitable home, assuming he is tame and healthy.
They would likely also worm and vaccinate him.
If he is being re-homed with other cats, we need to ensure he has no infectious diseases such as FIV or FeLV. This is done with a blood test.
As you have 4 cats who are already not keen on him, your home may not be the best place for him.
It can be tricky to introduce a male who has been recently neutered (and will still have some testosterone and Tom behaviours) to a household with just one cat, let alone four.
However, if you really want to take him on, it may be possible with a lot of hard work and keeping them all separate at first.
