The second the Dendrobium is sun burn from too much direct sun. Keep it in less light. It should recover easily without your need to do anything.
The first, the Phal, is in bad shape. It too may have been burned but there is secondary infections attacking the leaves.
Cut off all the infected areas. If there is new growth in the center of the crown you might save it but if that leaf is also bad the chances are slim. Phals need even less light than Dendrobium so if you were growing them near each other that was the cause of the damage.
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