Hi op, the hospital you gave birth in should have an infant feeding specialist. They should be able to give you a feeding/ pumping plan and support you with this. I'd also encourage you to join a local bf support group as lots of mums will have had similar experiences, many of the mums in my group exclusively pump or combi feed etc so any form of bf is welcomed.
I found eating lots of oats really helpful in increasing supply and I also found that looking at photos or videos of ds when pumping helped encourage let down. Some women get really stressed over the amounts they're expressing and stress inhibits let down so covering the bottles with socks so you can't see what you're pumping might help relax. Make sure you're warm and calm and not going to be interrupted, some breast compression beforehand can help as well. Make sure you're pumping regularly and I found that pumping at the same time daily was important for me. You can power pump, 10 min pump, 10 min break, 10 min pump 10 min break, 10 min pump to try and boost supply as it mimics cluster feeding. Tbh I'd be trying to pump 2 hrly day and night to mimic the way you'd feed... prolactin levels are also higher at night so you might find you get more/ better " quality " milk during the night. Flange size and comfort are really important you don't want to be sore or damage your nipples using the wrong size. I also found I needed to toggle the settings sometimes and starting gently and building it up was helpful. Plug in pumps are usually more powerful in terms of suction than wireless. I'd probably be inclined to try and go for a hospital grade pump if you haven't already. Lots of water and make sure you're eating enough.. take care of yourself- you're the cog that keeps everything else turning.
Congrats on your babies!!