I intend to do umrah with my wife and son and we are travelling from Madina in train to Makah. Where can we wear ihram as the train does not stop at meakat ?

The only way to wear it outside of the designated places is to make nathr. For example, you make a valid vow with God with the correct verbiage that if you arrive safely to Medina, you would wear the Ihram there before heading to Makkah.

لله علي ان
It is a promise to God upon me to