3 months old twins have ankle clonus (born 36w). it could be unprovoked and can last for 5-25 beats. the neurologist saw no issues (as all fine with their reflexes) but also said it should start to disappear. i see no improvement. should i worry?

No. Ankle clonus is a reflection of the maturity level of the kids nervous system. It is often present to some degree until the kids start to cruise/walk between 9-15 months after the progression of nerve maturity occurs. These are normal primitive reflexes. Find it in a 2 yo and I consider CP. Relax.

The birth history would be helpful. Did your twins require a NICU stay? Did they have any medical issues identified, other than late prematurity? If they are otherwise well, continue to monitor development and growth with your PCP.