Hello Potater,
Aside from having similar strengths, weaknesses and preferences, they should also tend to have similar physical features, as apparent in the case of twins.
However, the physical features are also dependent upon the Term and Face ruler of the Ascendant, among other things, which can be pretty sensitive to the change of time, as there are five Term rulers and three Face rulers in each sign. A 20-30 minutes difference in birth times is sufficient to change the Term ruler, assuming that the first person's Ascendant was at the beginning of the Term.
Another important thing is to note the Moon and its aspects, for it signifies the body and is the fastest moving...'planet'. Change or perfection of aspects will also change the body.
In some rare but interesting cases, we might also see a planet retrograde in one chart and stationery in another chart, and vice versa.
Needless to say, all this is also true for talents and preferences.
In the case of twins, they will likely be very similar in nature. But then there's nurture. Moreover, the objects or constructs in a natal chart symbolizes many things, signifying that there are several possible paths for a person to take. So twins can end up in different places though they are very similar in nature.
EDIT:
It would be interesting to check hospital records to look at how often this occurs