Piggies do not do play meets, for them every meeting is a full-on bonding session. You have done the full run up, so please commit and do it properly when you have a day's time. There is no 'magic wand' measure and there is no trick to make them get on. It all boils down to whether they are personality matched or not - and that is something that can only happen during the proper bonding process. Any stop-and-go is counterproductive for them as it means they can't get on with the real stuff.
It only makes sense if you are dealing with a piggy with major fear-aggression issues and even then you have to always take it just to the point where it gets too much for them; but in your case are clearly not dealing with thuis problem!
Here is our illustrated guide with lots of pictures and videos that takes you through the whole complex bonding process step-by-step with all the key behaviours and dynamics for every stage and chapters on the specifics of sow, boar, mixed gender bondings. Please take the time to read the link carefully and use it as a reference: Bonding and Interaction: Illustrated social behaviours and bonding dynamics
All the best!