Everything is fixable with console commands-

First, try force dismissing broken companions, you’ll need to get their refid first though (so maybe load an older save, or just search for the refid with the help command - ie. help mountbatten 4 npc to search for ‘mountbatten’ in refids that are classed as ‘npc’)

For reference, since I have it written on a post-it in front of me, Mountbatten is 082c1edc (08 may be different if londonworldspace.esm is in a different slot)

To force-dismiss Mountabtten-

prid 082c1edc
setconsolescopequest followers
emptyrefalias companion
setplayerteammate 0

To move Mountbatten to you-

082c1edc.moveto player

Try to get Mountbatten to join again normally, if he doesn’t, to force-enlist a companion-

prid 082c1edc
setconsolescopequest followers
forcerefintoalias companion