I know you said they are a year apart. What ages are they now. 1 and 2? you have puppy growing up the 4 month old coming into your home, becoming a young adult, stage of testing the waters of what they can get away with, bigger in size wanting to play rougher as well.. And the older one still not a full experienced adult with all the graces that come with age, still young adult as well, getting tired of a pushy puppy and wanting to set boundaries that the pup isn't so easy going to accept now. (two kids playing in the sandbox fighting over toddler stuff) mentality.
My smartest dogs are the ones that set boundaries that they are not a new pups playmate from day one. They always establish they not equal level free for all playmates. They are the ones that do better when a younger pup gets bigger and wants to be annoying pup still listens to them and still give respect. The other dogs that do the playmate with a pup have more difficult time trying to establish behavior boundaries when the pup gets bigger, so they over correct trying to get their point across, and the pup still thinks they only a playmate and keeps pushing. And it escalates from one, and the other pushes back harder as well
They still both need your hands on direct guidance at this age on how to handle themselves and living in your house. Yes separate, fall back on strict house hold schedule of interaction, dial up you OB skills and bonding through working with them one on one. Usually working on them as individuals they grow through the stage , restores peace an a sense of well being in the house hold as the norm. It's more exciting to look for opportunities to fight over something think that is why dogs get stuck in that for a daily routine. You want them to be focusing in on you and not what each other is doing. That is one of the things I work on, not to start looking at the other dog (none of your business) for me it always starts with focusing in on what the other dog is doing...
They need a consistent break for a while, break the cycle restore confidence for them that they not going to cause a fight or constantly be waiting to be challenged or attacked over something. Work on their focus to you, new skills they can perform individually, like sending one somewhere. (me it was back to the house) or (freeze) Hopefully in your pair as male /female it's a phase they not have the skills how to handle situations right now.