I’m glad they are getting on well.
Do be aware that fighting is very different to dominance. Dominance behaviours are normal but fighting is not and is bond breaking.
Please do look to get them a bigger cage as soon as possible. Being in a cage which doesn’t give them enough space (aside from the fact it doesn’t meet welfare requirements) to get away from each other can cause their bond to come under tension and can cause two piggies to fall out. One strong season without enough space to get away from each other could cause problems. Also ensure you have two hides and multiple of every other items and that all hides have two doors.
Do also check that they are both female. The shop may say they only sell female, but we sadly see so much
pet shop missexing that you should check their sexes yourself rather than rely on what you have been told
Dominance Behaviours In Guinea Pigs
Bonding and Interaction: Illustrated social behaviours and bonding dynamics