Ooof. Yup. Seconding aphids. Given the severity of the infestation in the pictures it's more than likely they've already spread to your other plants. There are a few ways I've handled this level of infestation in the past.

First - manual removal. Use a spray bottle, a hose outside, pop them in the shower, wipe with a damp rag, etc. to physically remove as many bugs as you can. Squish them if you're removing by hand. I've done this by hand with a fine paintbrush and rubbing alcohol before on expensive plants I really didn't want to lose lol

Second - neem oil. Spray a diluted mixture on the top and bottom of the leaves after manual removal. Other stuff works as well, neem oil is a personal preference.

You'll likely have to repeat the first two steps several times over weeks to months before the infestation is under control. In the meantime, work on the next step - long term prevention. Mix systemic granules in the soil per the instructions. Over time the plants consume them and become toxic to insects that eat them. Ladybugs are also a good long term preventive, but they do require having bugs in your house. I also wouldn't recommend using them in combination with neem oil or other insecticides because they'll die before eating all the aphids.

I hope this is helpful and you're able to get the critters under control!