5. Five pairs of twin siblings participate in the activities of $k$ groups. If the rules are: (1) Twin siblings are not in the same group; (2) Any two people who are not twins have participated in exactly one group together; (3) One person participates in only two groups. Then the minimum value of $k$ is $\qquad$ .
5. Let the five pairs of twins be:
$$
\left(A_{1}, A_{2}\right),\left(B_{1}, B_{2}\right),\left(C_{1}, C_{2}\right),\left(D_{1}, D_{2}\right),\left(E_{1}, E_{2}\right) \text {. }
$$

Only the following grouping method satisfies the conditions and makes the number of groups $k$ the smallest:
$$
\begin{array}{ll}
\left(A_{1}, B_{1}, C_{1}, D_{1}, E_{1}\right), \quad\left(A_{1}, B_{2}, C_{2}, D_{2}, E_{2}\right), \\
\left(A_{2}, B_{1}, C_{2}\right), & \left(A_{2}, C_{1}, B_{2}\right), \\
\left(B_{1}, D_{2}\right), & \left(C_{1}, D_{2}\right), \\
\left(B_{1}, E_{2}\right), & \left(C_{1}, E_{2}\right), \\
\left(D_{1}, B_{2}\right), & \left(E_{1}, B_{2}\right), \\
\left(D_{1}, C_{2}\right), & \left(E_{1}, C_{2}\right), \\
\left(A_{2}, D_{1}, E_{2}\right), & \left(A_{1}, E_{1}, D_{2}\right) .
\end{array}
$$

In total, there are 14 groups.