You can have four Single Strike Urshifu V and four Rapid Strike Urshifu V in your deck because "Single Strike" and "Rapid Strike" are part of the card name for these cards. Also, Single Strike Urshifu VMAX must evolve from Single Strike Urshifu V (and vice versa for the Rapid Strike ones).
Source: Battle Styles FAQ; TPCi Rules Team (2021-03-18)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH5_85
SWSH5_85
SWSH5_86
SWSH5_86
SWSH5_87
SWSH5_87
SWSH5_88
SWSH5_88