Homeowner cannot figure out how to connect a new water filter system to existing 70-year-old galvanized steel pipes using PEX due to conflicting advice, hard-to-find fittings, and difficulty identifyi

Homeowner cannot figure out how to connect a new water filter system to existing 70-year-old galvanized steel pipes using PEX due to conflicting advice, hard-to-find fittings, and difficulty identifying the correct connectors.