I've blended and bonded over the years, had sucesses and failures.
I bonded a piglet boar with a bereaved adult.
2 sows with a boar we had neutered.
New boar with the sows when the other boar died .
A doddle , I thought .........until I met GP8 
We had a trio ( 2 sows+ boar) , got 2 more sows.
They would not bond .
We kept a 3+2 set up.
The older sows died , we tried to bond the boar ...GP8 had none of it.
He stayed side-by-side for 18 months, till GP8 died.
We bonded the boar+ remaining sow , they had a couple of months of marred life till he died .
We now have one girl. She was tricky to bond with him, and was sometimes snippy with GP8 .
So we're keeping her indoors (she's near DD room and there's no door on the piggies bedroom )
Our boar was very rumbly living next door to them , he had his own space and often slept next to the divider (we could tell by the pooh pile) . We used to give him a little cardboard box of hay next to the bars so he could sleep there and chat to them.
But we couldn't put him with GP8 for his own safety , she literally went for him, I have never seen such viciousness in a piggie. (we tried a few times them admitted defeat)
GP8 was the sweetest little animal otherwise .