This phase Ib/II trial tests the safety, side effects, and best dose of navitoclax in combination with venetoclax and decitabine in treating patients with higher risk myelodysplastic syndrome (MDS) that has come back after initial treatment or was not responsive to initial treatment. This study will also look at the effectiveness of the treatment combination and patient's quality of life while on these medications. Navitoclax is an oral drug that works as an inhibitor of the BCL-2 family of proteins, which are often overly expressed in a wide variety of cancers and are linked to tumor drug resistance. This drug blocks some of the enzymes that keep cancer cells from dying. Venetoclax is an oral drug that works as an inhibitor of BCL-2 proteins that works very similarly to navitoclax by blocking the action of a certain proteins in the body that helps cancer cells survive which helps to kill cancer cells. Decitabine is an intravenous drug. It is a hypomethylating agent which means it interferes with deoxyribonucleic acid (DNA) methylation. DNA methylation is a major factor that regulates gene expression in cells, and an increase in DNA methylation can block the genes that regulate cell division and growth. When these genes are blocked the overall result allows or promotes cancer as there is no control over cell growth. Decitabine stops cells from making DNA and may kill cancer cells. Participation in this trial may improve the understanding of both chemotherapy response in MDS and mechanisms of resistance to current therapies.