Let's say that there are some humanoid mammals that can talk like humans, and their voices are about the same (so not really high or low pitched). Some of them have different tongues too, really thin but long. Would they be able to make the sounds from their throats or something? So far I kinda have them do that, so they slightly open their mouths and talk normally without opening and closing them the way humans do, but is such a thing biologically accurate?
Use a syrinx
Birds like parrots and crows can produce human-like speech, despite lacking lips, teeth, or flexible tongues. This is because instead of the relatively simple vocal cords of mammals, birds have a syrinx - a set of tubes close to where the trachea splits into the lungs (basically in the middle of their chest instead of the neck) surrounded by muscular rings that can open and close in various complex patterns, giving them even more capability for sound production than humans without using their mouths at all.
The problem is that you said want these creatures to be mammals. The syrinx is a highly advanced organ that exists only in birds, and has a completely different origin than the simpler larynx - the chances of another branch of animals evolving the same structure is fairly low.
The precise origin of the organ is not known - crocodiles have a larynx, and so far no evidence of a syrinx in non-avian dinosaurs have been found, but some of the earliest birds did have them. The idea of a theropod dinosaur with both hands and a syrinx, though iffy, is not completely out of the question (one theory is that the syrinx evolved due to the long necks of birds, and theropods did have long necks).
Perhaps your creatures are not actually mammals, but humanoid descendants of raptors!