Character types are never consistent and there is always some variation, but if I had to average their types based on the main characters it would be:
Eric: ISFP 4w3
He is actually quite sensitive and is dedicated to things that are important to him: family, friends, fantasy and his relationship. He doesn't really stray much from the important things to him (Fi) and simply wants those things to work out for the best without the reprecussions of his parents. He usually goes to people for advise though on how to realize these things (inferior Te). His fantasy desires are more geared toward sensory things (Se) and isn't overly idealistic with them (as expected in INFPs). This fantastical life is more about things that are according to his unique vision and form of self-expression (4w3).
Donna: ESTP 1w9
Although she may come across as rational in the intuitive sense, she seems to still focus more on risk-taking and what sort of experiences would maximize the most sensual pleasure rather (Se), but focuses on the right way of doing it. She cares about social dynamics and how others come across to her and how she comes across to others (Fe) [esp. to Eric], but also seems to be able to figure out if the plans the group does makes sense (Ti). If you think about her role, she seems to be the wise, ubermensch type who seems to be the moral critic of other people's actions, where other's vices stand out more than hers (1w9).
Hyde: ISTP 7w8
Of all the characters, it is rather clear that Hyde is the clever one who seems to figure out what works and what doesn't for the group. He has an original way of thinking which diametrically opposes how one ought to think in accordance with pre-established rules (Ti). Although many might perceive this as intuitive, he is very stubborn in his insights (tert Ni) and seeks more to see how practical ideas work in action (Se). He is more inclined though to start trouble for the sake of his entertainment and fights the system to gain 'freedom' (7w8) and doesn't like to be sensitive, but on rare ocassions has a soft spot (inferior Fe).
Kelso: ESFP 7w6
Very rarely does Kelso think about the consequences of his actions (inferior Ni), but always has the need to act on sensory impulses for his own personal satisfaction (Se). He is usually the most inclined member of the group to get himself into situations that are the biggest stunts. He does this mostly for entertainment, but also for his entertainment to be accepted by other group members (7w6). Most of his decisions are focused more on what personally impacts him and rarely on how it affects other people, but when people don't act in accordance to what he wants from them he will change his behavior in efforts to reach his goals (Fi). This is especially the case in relationships.
Jacky: ESFJ 3w4
Although her demeanour may come across as self-invested and unfocused on how other's are impacted, Jacky really cares about how her appearance comes across to others more than anyone else. She idealizes being seen a certain way and does so by fitting into groups (e.g. cheerleader phase) and then flaunting how she is much more successful than others at it (3w4). It might seem that her lack of concern with others is ESTJ, but generally her control for others manifests in celebrating her pride as strongly to others as she does to herself (Fe), though she is very particular about her preferences/style and how they should appear (aux Si).
Fez: ISFP 2w3
The quiet, yet somewhat eccentric foreign kid, Fez is probably the most sensitive out of the group. Although he doesn't always express it, he always seems to care about his relationship with other people and how he can act toward other people (Fi). Don't all 'foreign kids' just want to fit in? He often gets jealous when people don't pay attention to him or recognize his efforts for other group members (2w3). He also does have interests in more sensual pleasures: his obsession with candy, collecting girl's panties etc. (Se). Although he seems to want to be recognized for his actions, he can be rather aloof to the social vibe - which is indicative of a lack of Fe; which tends to get confused for 2s.
Kitty: ISFJ 9w1
This typing may be more confusing and a mish-mash than other types, but Kitty is generally a down-to-earth, homely person who always seems to know what sort of qualities can emerge together to create a stable and calm environment. Her persuits are more based on what entities go well together to create the 'perfect recipe' (Si). I mean this both figuratively and literally, as she spends her time cooking and sewing a lot. But she always tries to tie people together and make sure that there is no conflict among them, but sometimes loses her cool doing so (both 9w1 and Fe). Other possible types might be ESFJ, INFJ and 2w1 or 1w9.
Red: ISTJ 8w9
There is always a sort of fierce, militant vibe from Red, while he focuses more on what personal comforts and right aesthetic combinations work for him. Though Red may come across as more domineering and controlling for the average ISTJ, this is fueled due in part mostly to his need for people not to get in his way or cross his boundaries (8w9). He always has hard skin, but discretely does so not by actively putting himself in situations that he wishes to implement as goals, but by maintaining his existing environment by "taming the shrew" (Si). He has certain ways that he believes makes sense to him, which can be seen in his need to fix things, but never goes overboard with them (aux Te).
Bob: ESFP 6w7
He is a bit harder to assign a type for, but he is usually seen as the upbeat character who likes having a fun with new experiences (Se), yet can be somewhat sensitive to his needs and what he wants for people that matter to him like Donna (Fi). But he always has a tough time trusting Eric and his relationship partners, but wants Donna to blend into a secure, stable environment (6w7).
Laurie: ESTP 7w8
She is not a very developed character, but is known for her need to be in charge, but also to get into particularly promiscuous situations that she finds to her personal satisfaction (Se and 7w8). She also usually has some sort of judgment toward Eric or Hyde, but usually this is implemented in the battle of wits than it is in anything else (Ti) even though she does so by influencing others (Fe).