Adding a third boar to a bonded pair is not recommended.
Usually what happens when adding a third boar is that the newcomer is rejected. But it can also be the case, as has happened with you, that the bond between the original two is broken. The other thing is that it breaks the bond of the original pair plus they reject the newcomer meaning three single boars.
Things will be highly unlikely to improve between them and may in fact get worse and result in fights
We would recommend that you separate them so John is not at risk of being bullied or injured due to fights if Alex feels he doesn’t want him in his territory. Yes if you can get a fourth piggy to bond with John then it would be good to do so. However, it’s also fine for him to live as a single but alongside the cage of Alex and David.
Please do also be aware that as David is only 5 months old and has yet to teach peak hormones, while at the same time Alex is still a teenager, please do prepare for the possibility that hormones from David may also pose a risk to the bond between Alex and David.
Please do have a backup plan in mind for Alex and David just in case things don’t work out between them. Sometimes out of attempting a boar trio, all bonds are broken and you can end up with three single piggies.
Please ensure the cage of a boar pair is 180x60cm on a single level. Upper levels do not count towards the cage size and ramps and upper levels can cause problems with boar pairs if the ramp is claimed as territory of one of the piggies.
If John is to remain single ensure his cage is at least of 120x60cm. Make sure it is beside the pair so they can still have constant interaction between the bars only. This will stop John from becoming lonely.
If John is to have a friend then his cage also needs to be 180x60cm.
(The cage size needed to attempt a boar trio goes beyond sizing allowances - you would need to have a cage measuring at least 300x100cm if you are going to risk keeping the three of them together - as I say though, things are unlikely to ever improve and may escalate into a worse situation).
To add, we do not recommend that food bowls are ever used. Not only because the use of a bowl can cause hogging, but the main reason is that using a bowl removes their ability to use their natural foraging habits. We recommend scatter feeding veg amongst loose piles of hay so they can use their foraging abilities to search for their veg. Piggies spend large parts of their day foraging whereas using a bowl is a rather mindless activity and makes veg time over very quickly.
The two guides below explain more
1 Singles and Pairs
Singles: Challenges and solutions for different singles situations (link)
Pairs: A closer look all possible pairings (link)
2 Trios and More by Gender
Boars
- Trios and quartets - Why better avoided
- Large Groups...
1 Common myths and misconceptions
2 The different ages (including teenage)
- Important biological facts
- The formative 'School Weeks' (3 weeks - ca. 4 months)
- The Teenage Months (ca. 4-14 months)
- The Adult Years (ca. 15 months - ca. 4-5 years)
- The Golden Age (ca. 4-5 years until end of life)
3 What do boars need? (List of boar dos and don'ts)
- Space, space and more space!
- Respecting the hierarchy
- The 'one for each...