I keep getting this message whenever I try to bring more then one passenger into my shit.

Sensors indicate the items you [or your party] are carrying will overload the capacity of the YT-1760 [RC] Euphemia. Please discard some items before entering.

Although, my passenger capacity is only 2/8 right now, and this is the status of my ship's capacity.

No Damage to Weight Capacity
--
Used Weight Capacity
0/3 Tons
Remaining Weight Capacity
3 Tons
No Damage to Volume Capacity
--
Used Volume Capacity
0/10 m3
Remaining Volume Capacity
10 m3

I'm assuming that I should be able to fit the other two npcs into my ship, but I wanted to check here if I'm missing something before going to the bug base.

It's talking about equipped items, I believe. What are you wearing?

Large backpack, imperial navy uniform, heavy belt, and a CVI. But I'm still at half of my own capacity.

It's not your capacity - it's what the ship can carry.