You can travel on one ticket in multiple trains but subjected to - All trains runs on same route and all trains have stopages at stations used on same date. Also buy a SF ticket, this will allow you to use Exp and SF Exp trains (except special trains like Raj, Duranto etc).
Answer to your que: you need to board trains on same date, you cant board unchahar today and swaraj tomorrow. Also SF ticket will be valid in unchahar as well.