The Triple Missionary Threesome position comes with built-in pleasure for the penetrating partner through intercourse. We recommend that this position be reserved for people with less chronic pain and the ability to thrust. We also recognize that, for some disabled folks, this position does not work.
For the other two partners, however, sexual satisfaction isn't built into the equation. As the middle partner will likely be using their hands to hold up their body weight, the penetrating partner can provide a helping hand by reaching around to play with the middle partner's clitoris or penis. Alternatively, the bottom partner can pleasure the person in the middle—or use their hands to pleasure themselves.
If the constant body motion and excitement makes it hard to focus on dedicated finger movements, don't forget about bringing sex toys into the Triple Missionary! For example, if the bottom-most and middle partners both have a clitoris, you can tuck a large wand massager between them to provide easy, minimal-focus stimulation for both people. (This can work just as well for those with a penis; but it may be a new type of stimulation that penis-owning people may not be as familiar with!)
As the Triple Missionary mixes the standard missionary and doggy style positions together in a group-friendly way, most people will easily understand how bodies fit together for this position. However, with people's knees supporting most of the weight in this position, we recommend performing it on a soft bed or sex furniture—or enlisting the help of some pillows to soften pressure points on the joints.