So, on jorats' suggestion, I decided to try a neutral intro before having Peter neutered (my four have been split into pairs for months after Peter's aggression towards Fred).
It went great. 30 minutes of relaxed interactions, mutual grooming for all! A tussle broke out between Fred and Peter, and I separated them in a second.
but here are my pictures from the event:
[img=center:h7nyann6]https://lh6.googleusercontent.com/-WIoHW5KqIjs/TyzEOauYDKI/AAAAAAAAC2M/7uWxnkxftOQ/s400/IMAG0049.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh6.googleusercontent.com/-Glf29cTfs3c/TyzE80gqkjI/AAAAAAAAC2I/4rqMnn__VGE/s640/IMAG0051.jpg[/img:h7nyann6][img=center:h7nyann6]https://lh5.googleusercontent.com/-QXAL6ndsCFE/TyzIdkXKydI/AAAAAAAAC2A/dpdpVgGtDfk/s400/IMAG0081.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh4.googleusercontent.com/-KNYTqDSBcyg/TyzHfaX270I/AAAAAAAAC14/Kp_i4v33fiE/s400/IMAG0062.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh5.googleusercontent.com/-ebxLo6V8Jso/TyzH8DeU27I/AAAAAAAAC1s/MS9JF29xyUI/s400/IMAG0069.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh4.googleusercontent.com/-_ZivYl7QcCg/TyzIn41YwmI/AAAAAAAAC1o/IcyHrz80X5M/s640/IMAG0084.jpg[/img:h7nyann6]
The last one is at least 5 minutes before the fight broke out between them. Peter is on top of Fred there, and they're the only two who ever had any problems. Peter was relaxed, but Fred was stressed out the whole time. He tried to jump out of the tub several times. Fred did take his turn grooming each one of the others though!
It went great. 30 minutes of relaxed interactions, mutual grooming for all! A tussle broke out between Fred and Peter, and I separated them in a second.
but here are my pictures from the event:
[img=center:h7nyann6]https://lh6.googleusercontent.com/-WIoHW5KqIjs/TyzEOauYDKI/AAAAAAAAC2M/7uWxnkxftOQ/s400/IMAG0049.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh6.googleusercontent.com/-Glf29cTfs3c/TyzE80gqkjI/AAAAAAAAC2I/4rqMnn__VGE/s640/IMAG0051.jpg[/img:h7nyann6][img=center:h7nyann6]https://lh5.googleusercontent.com/-QXAL6ndsCFE/TyzIdkXKydI/AAAAAAAAC2A/dpdpVgGtDfk/s400/IMAG0081.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh4.googleusercontent.com/-KNYTqDSBcyg/TyzHfaX270I/AAAAAAAAC14/Kp_i4v33fiE/s400/IMAG0062.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh5.googleusercontent.com/-ebxLo6V8Jso/TyzH8DeU27I/AAAAAAAAC1s/MS9JF29xyUI/s400/IMAG0069.jpg[/img:h7nyann6]
[img=center:h7nyann6]https://lh4.googleusercontent.com/-_ZivYl7QcCg/TyzIn41YwmI/AAAAAAAAC1o/IcyHrz80X5M/s640/IMAG0084.jpg[/img:h7nyann6]
The last one is at least 5 minutes before the fight broke out between them. Peter is on top of Fred there, and they're the only two who ever had any problems. Peter was relaxed, but Fred was stressed out the whole time. He tried to jump out of the tub several times. Fred did take his turn grooming each one of the others though!