Moms and babies can be a little loud if one of the lambs wanders too far off, loses sight of the mom and then panics. Mom will call to it to get it to come back close. This gets less as the lambs get older and start to graze themselves. Expect them to baa at you when they see you come with hay/grain, or just to say hi.
As far as the fence goes, I have only ever seen sheep behind field fencing with one strand of electric or behind 2 strands of electric. If there is something tastier on the other side of the fence they like to lean on the fence and can push it over.
I would supplement some hay, depending on the forage mixture you have protein/energy/calcium levels may not be enough, especially for mom trying to make milk for twins. Also, some breeds of sheep are "easy keepers" compared to others- what breed are these sheep?