They are normal dominance behaviours, it doesn’t warrant separating them at all. At four months old they are just hitting their hormonal teens. You are going go see hormone spikes and dominant behaviour until they are 14 months of age, but in reality you will see it throughout their entire lives.
You only separate if they have a blood drawing fight. In that situation it’s immediate and permanent separation, with their cages next to each other and they must not have physical contact such as during playtime again (to separate playtime’s).
Character compatibility is the key to a successful relationship - one must be dominant and one submissively to be able to form a working hierarchy. The fact you say one is doing it more than the other sounds like they may have a hierarchy.
A bigger cage is essential - two boars need more space and require a cage measuring 6ft x 2ft (180cm x 60cm) as anything smaller than that can cause problems in their relationship (although cage size is secondary to character compatibility in terms of a functioning relationship).
When you give them their bigger cage you need to be careful - a change in cage constitutes a change in environment and a change in territories which on its own can set off dominance and territorial issues. Ensure you use soiled bedding from their current cage and move it into their new cage as that way it will still smell of them and can help keep them calmer.
You need to have two of every item, and only used hideys that have two exits (nothing enclosed as one piggy can corner the other which can lead to problems). Always respect the hierarchy and therefore always handle and do everything for the dominant piggy first.
Below are some boar specific guides and some behaviour guides. Do give them a read.
A Comprehensive Guide to Guinea Pig Boars
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
Dominance Behaviours In Guinea Pigs
Bonds In Trouble (this one doesn’t seem to be relevant to your current situation, but it is a good idea to know exactly what you are seeing in terms of their behaviour so you can spot quickly if things take a turn for the worse)
