It's not clear. I've always assumed that the GTVA has some number of frontline fleets, each one centered on a destroyer, supported by cruisers and corvettes; possibly also a second destroyer. It would also have local forces, likely on the same model as fleet but one to a system, and war reserve ships in mothballs. For myself, I've always assumed fleet size to be 20 to 25 combatant ships. Vasudan frontline Battlegroups would be slightly smaller, 15 or so combatant ships, but their local and war reserve forces would be of similar size to Terran ones.
About the PVN we know very little. However, the GTA seemed to assign fleets to a "home system" so to speak (meaning probably larger), so they could be rotated off the line to rest, rebuild, and refit when needed, whereas GTVA fleets seem to be concieved of as more mobile entities (meaning probably smaller), likely because they are meant to move to meet a Shivan attack; the GTVA military, lest we forget, was almost certainly constructed and trained to meet a second Shivan invasion.