Well, I think you’ve been doing the right things. Some cats just take much longer, and I honestly think when it’s two cats who are scared together, it’s harder to help them, because they reinforce each other’s fears sometimes. We had a pair of siblings like you describe a few months ago, and it took them 2 full months to really get comfortable with us–and one never did get comfortable being picked up. But helping them be less scared is definitely doable–just might take you much more time than it has previously.
A couple things to keep in mind–try to keep yourself “small” when you approach them–don’t walk over to them for pets in a way that towers over them. Sit on the floor when you can. Reach out palms down, fingers closed so your hands look less like claws about to attack.
Other things to start trying–whatever toys are their favorite, those only come out when one of you is around. And when you’re around, actively play with them with those toys. If there is a wand toy they like (or if you haven’t tried wand toys yet, get one), play with them until they are tired/very distracted playing with the toy. Over the course of a few days, get the wand toy closer and closer to you. Sit with your legs sticking out, and get them to chase the wand toy in a way that makes them need to run over your legs–they’ll probably balk at first, but eventually will want the toy enough to do it. Don’t try to pet them then–let them know that running over your legs is an interaction they’re in control of, especially the first few times. Once they’re running over your legs without hesitation, then start trying to have the toy stop in a spot where it’s close enough for them to pounce/catch it *and* for you to sneak in a quick pet of their back/head/side. Continue playing like this over several days until they let you pet them without shying away.
If they’re more treat motivated, then treats are only for when they’re choosing to interact with you. Try sitting on the floor and creating a line of treats that lead to your foot or your leg. Get them comfortable eating a treat next to you. Once they are, then try a line of treats leading *onto* you. A single treat on your leg. If they eat it, replace it and see if they eat it then. Once they’re comfortable doing that, repeat, slowly moving the treat to different places on you. See if you can pet them while they eat the treat. All of this might take a few days, or it might not; either way, repeat this process until they’re comfortable approaching you for a treat and let you pet them when they eat it.
Try to pet them and interact with them when they’re eating, but try to do it in steps over several days–you want them to associate people/petting with the things they like, including food. Start with just sitting near them while they eat. Then reach a hand near them. Then try petting them. Once they’re more comfortable with you petting their back/head/tail, then you can work on petting sides/neck/and eventually the belly (as they’re standing, not while they’re laying down), or getting them to get in your lap (you can probably use treats for this, too).
Start with one hand petting before you try petting with two hands. Once they’re okay with two hands petting, you can try picking up, but only a little bit–practically just a scoot instead of picking up. Once they’re okay with that, then maybe a quick pick-up/scoot into your lap, or to your side. The most important thing is to never rush them, and if they react badly to something, just go back a couple steps from where you were and start over. Let them build trust that you’re not going to push them too fast, and that if you do, you’re going to back off for a bit.
It’s very possible that one of the cats will do better with these steps faster than the other, and that’s okay–they will be a bridge for the other cat to see that it’s okay. They may also do better with one of you than the other, and that’s okay, too. If you haven’t tried using Churu lick sticks as a treat, you might want to try those, because they are a game changer in terms of getting frightened cats used to being near people’s hands.
I hope this helps! Feel free to email me if you need more advice.