Fundamentally a sow will only produce milk and thus able to suckle if she has been pregnant. If there were two sows in the same sounder that gave birth pretty close together then could be shared suckling, but generally a mother will only suckle their own young. They will take themselves off to give birth and will only rejoin the sounder after a few days once the piglets are a bit stronger and well bonded to her.
But once in the sounder there will typically be the lead Matriarch, together with other younger breeding and non breeding females and collectively they will look after the sounder which will consist of this years piglets, as well as uberloafers (teenagers, who just hang around and cause trouble). The big old females run the sounder, and keep order. If you shoot these old females you end up with lots and lots of damage as the youngsters and uberlloafers just run amock.
Once the young males get towards maturity they will get booted out and will then hang around in batchelor packs and will tend to roam quite widely looking for breeding females that are not under the control of a big Keiler - a breeding male.
The Keiler's keep close to the breeding groups, but tend to keep to back.
So when you have a load of pigs appearing you will tend to have a number of mature but not Matriach sows leading out, followed by the big Matricach (identified by large size and big arse) with lots of piglets and other youngsters, all around will be the teenagers. And a few moments later will be the Keiler - they only come out if the coast is clear. When a big group appear it takes experience to be able to quickly sort out what is shootable and what is not, and also to shoot something that is clear of the others.