First, the harness idea is certainly worth exploring so give it a try and see what happens.
Second, yes, the dynamics in the household probably are changing. Lion and Bear have the same relationship with each other that Tink and Grayson had - it seems to have been restored between them, but the relationship they both had with my older cat Tristan changed. Tristan used to be the alpha cat and it had never been challenged until the night when the stray 'attacked' at them through the window. Lion took on the role of alpha, although Bear did some jockey-ing for it as well. Tristan was confused and had no idea what was going on and basically as long as there are no problems they can co-exist comfortably, but if there is a problem Lion moves into alpha mode. Aggression happens if one of the other two challenges it. I suspect that Grayson is deciding that he can do the alpha role as well and you will have Grayson and Tink jockeying for that alpha position. They will have to rework their own dynamics and a lot will depend on how strongly each insists that he be alpha. Since they had such a good relationship before - like the one between Bear and Lion in many ways - there is a lot of positive interaction there from previous so once they begin to 'chill out' again, there is a good chance to you will be able to restore some of that. Do remmeber that even though it has been a few days they are all still hyper and on edge and it doesn't take much to have one of them tumble over so be really alert to body language and act quickly to intercept any aggression before it actually becomes aggression. Have a blanket available to toss over Tink even when he is in the harness because you don't want him turning on you if he does get aggressive. Try and keep him in the company of one of the safe cats as well and gradually increase the time he spends with them outside of Gray's company.
PS - one other useful bit of advice I received - if you need to pick up a cat to prevent a violent outbreak, pick up the alpha cat not the one he is attacking. If he hasn't become aggressive and is just doing the glaring and beginning to posture a bit you can prevent an outbreak that way. If he is already into aggressive mode - fur raised, tail puffed, stuff like that, touching him will set off the aggression so that is when you use the blanket instead.