How can I convert this chair into a porch swing?

Hi Margie: Geeze, those legs look awful :( If you want to make swinging chairs out of them, I'd get a piece of wood the same depth as the chair (front to back), but about 2 or 3 inches wider on each side, and attach a brace board, like a piece of 2x 4, to each side, from back to front on the bottom of this. Then I'd drill holes in both pieces, at least an inch and a half from the back and front and put a rope or chain through the holes, making a ^ shape, the top connecting to whatever you are going to use to attach it to the beam. Do this to both sides and all of your chairs. You can paint the wood to match or contrast with your cushions. Good luck

What exactly is broken on the chair?

If the leg supports have rusted all the way through, I would be concerned about the safety of using the chair as a swing. Perhaps look at other swings and incorporate their use of new lumber along with just the arms and back of the chair for "decor" on the wood structure?

I’d make a wood bottom Out of 3/4” exterior plywood the size of the bottom plus the over lap of each arm (the entire width) and add about a foot. Then paint it to match if necessary add a cross brace under the seat to bring the chair bottom down so it is flat . Glue the seat to the brace to the plywood then screw through each side of tHe whicker into the brace and from underneath from the bottom to the brace. Drill 2 holes into the bottom board on each side. Touch up paint if needed. Anchor strong screw eyes into the rafters running rope through the back left hole with the end knotted well up through the Screw eye back down to the front hole across the seat bottom up through the right front bottom hole back down the right back hole and knot or secure it well underneath . It sounds complicated but is really simple. You will end up with a rope triangle on both ends and the same rope across the bottom under the front two holes. The continuous rope should make it stronger as long as the rope is the correct weight and the back rope ends are secure. You could add big washers between the knots and the bottom board if you choose to add more strength. Some rope stretches so selecting the rope at a marine store or good hardware store would be best. I would choose a rope rated for at least twice the weight of whoever might sit in it even though the wait would be divided over the base! I have ten grandkids and grew up when twenty people would try to fit into a Volkswagen bug.lol

Betsy is spot on. You need to brace the chair using 2X4 all around/front, back and sides. Then either pass the chain under chair on sides or attach heavy duty hooks(similar to cup hooks) to attach chain. Then run both ends of chains to a heavy duty hooks in ceiling beams and attach chains to that. Keep in mind that the chairs will be supporting 100+ pounds. Look for hooks that have a long screw shank. By using longer piece of chain you can adjust height and angle of swings. If you have extra heavy guest you may have to ask them not to sit in swings and keep an eye on any kids that sit in them.