How to deal with "Split" party?

[MasterMercury]

So here's the situation.

My large party of 9 is currently in a huge underground fungal jungle. In the jungle are two warring clans, the Kuo-Toa and the Quaggoths. The Kuo-Toa enslave the Quaggoths and the Quaggoths eat the Kuo-Toa.

The party is traveling through, using the underground as a passage into Hobgoblin territory. One night, as they rest, half of them are abducted by Kuo-Toa, and the other half wake up and met the Qs.

Team Kuo-Toa was sent in a mission to guard an isolated camp . Team Q is sent to attack the camp, but instead kill the Q allies sent with them. The party reunites at the settlement. However, a third of the party breaks off, stuffs the Quaggoth slaves of this camp into a bag of holding, and run into the woods.

Now, 2/3 of the party are together, and want to move on.
1/3 are in the jungle, freeing Quaggoth slaves to build their own army to kill the "evil fish-people".
Im trying to balance between them, but I keep feeling that I'm not giving the 2/3 party enough to do. It's gotten to the point where they are just xp farming in the jungle, fighting giant boar for fun.

TLDR
How can I balance between a larger party that wants to move on, and a small party that wants to stay and do something?

[Tanarii]

Run two separate sessions.

[Cespenar]

If you're short of time in general, just speak with them OOC and brainstorm on how you can bring the party together, so that everything can run more smoothly.

Otherwise, just run them separately. Run a scene for group 1, and then one for group 2.

If there's another DM candidate in the group (preferably from the larger party), promote them to co-DM the smaller group while you DM the larger group.

[RickAllison]

I second the idea of DMing the two separately. Switching between the two is great for shorter times like a trap separating them, but this is a dedicated split campaign right now. Talk with your 2/3 to see if there is any way they would see their characters getting involved, and otherwise just focus on the smaller party until they finish the arc. Then you can figure out how they both will get together. But trying to figure out things for both will not satisfy anyone.

[Fishyninja]

If there's another DM candidate in the group (preferably from the larger party), promote them to co-DM the smaller group while you DM the larger group.
Elegant Solution. *golf applause*

[eastmabl]

If there's another DM candidate in the group (preferably from the larger party), promote them to co-DM the smaller group while you DM the larger group.

In a similar vein, if you know someone from outside the group who wants to DM, you could approach them about a short run DM gig.