Cast iron sewer pipe fittings

Do it right cut it out (rent a soil pipe cutter or us an angle grinder with a thin cut off wheel) and replace it with Pvc and some fernco’s. Just cut above and below the cast wye by 6”-8” so you can glue a piece of pipe in bell of the pvc wye that way you will have a common outside diameter for the fernco’s to slide onto. Anything else is just a temporary fix. If it was me i would start replacing as much of the old cast iron pipe as you can get to.