That is on the high end of weight gain, but it is not uncommon when piggies hit a new loving home.
As they also have plenty of exercise, there is nothing to worry about! They may stop growing a bit sooner once they hit their individual ideal adult weight any time after 6 months old. I found that when my baby Telyn hit the kilo at 6 months old - she stopped growing quickly soon after that and went on at a much slower rate.
PS: they are a lovely pair!