"Spins in gate-defined silicon quantum dots are promising candidates for implementing large-scale quantum computing. To read the spin state of these qubits,- the mechanism that has provided the highest fidelity is spin-to-charge conversion via singlet-triplet spin blockade,- which can be detected in situ using gate-based dispersive sensing. In systems with a complex energy spectrum,- like silicon quantum dots,- accurately identifying when singlet-triplet blockade occurs is hence of major importance for scalable qubit readout. In this work,- we present a description of spin-blockade physics in a tunnel-coupled silicon double quantum dot defined in the corners of a split-gate transistor. Using gate-based magnetospectroscopy,- we report successive steps of spin blockade and spin-blockade lifting involving spin states with total spin angular momentum up to S=3. More particularly,- we report the formation of a hybridized spin-quintet state and show triplet-quintet and quintet-septet spin blockade,- enabling studies of the quintet relaxation dynamics from which we find T1~4 mus. Finally,- we develop a quantum capacitance model that can be applied generally to reconstruct the energy spectrum of a double quantum dot,- including the spin-dependent tunnel couplings and the energy splitting between different spin manifolds. Our results allow for the possibility of using Si complementary metal-oxide-semiconductor quantum dots as a tunable platform for studying high-spin systems. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the ""https://creativecommons.org/licenses/by/4.0/""Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title,- journal citation,- and DOI."