Congratulations on your new piggies.
The correct way to bond is to put them all in a neutral territory bonding pen for several hours with no hides, only hay and water, so they can form their initial relationship.
After those few hours in the bonding pen, if all goes well, you can move them into their thoroughly cleaned out cage together to begin their life as a new herd!
It will take them a further two weeks to fully form their hierarchy and during that time you will see dominance.
Bullying is a very different thing and means the relationship has failed.
Bonding is not something to be done over several separate sessions, it should be just a one time event seen through to conclusion on that one day. Piggies should not be separated repeatedly as this interrupts their process and means they have to start from the beginning each and every time. This is stressful to them. The only time a bonding session should be ended and restarted is in cases of fear aggression in sows.
Any interactions when being held or when in a separated cage is not bonding. They need to be able to rumble and mount each other etc to form their relationship and hierarchy.
What you can do is have them live in a side by side cage for a few days prior to the actual bonding day to get to know each other.
Make sure the cage is big enough - that is a 180x60cm (minimum) or a 6x2 c&c - and that you have four of every item.
If the new piggies did not come from a reputable rescue centre, then they should be quarantined in a separate room for two weeks before bonding day. You should also get a vet check.
Also make sure, if you haven’t already, to double check they are definitely both sows.
We can’t know what is wrong with the feet, given we cannot see it, but any open wounds are of concern for bumblefoot and require urgent vet care.
Bonding and Interaction: Illustrated social behaviours and bonding dynamics