  We find a four-parameter family of coupled Painlev\'e VI systems in dimension
four with affine Weyl group symmetry of type $A_7^{(2)}$. This is the first
example which gave higher-order Painlev\'e equations of type $A_{2l+5}^{(2)}$.
We then give an explicit description of a confluence process from this system
to a 3-parameter family of coupled Painlev\'e V and III systems in dimension
four with $W(A_5^{(2)})$-symmetry. For a degenerate system of $A_5^{(2)}$
system, we also find a two-parameter family of ordinary differential systems in
dimension four with affine Weyl group symmetry of type $D_4^{(3)}$. This is the
first example which gave higher-order Painlev\'e equations of type $D_4^{(3)}$.
We show that for each system, we give its symmetry and holomorphy conditions.
These symmetries, holomorphy conditions and invariant divisors are new.
