Learn to help yourself-you will also need that when travelling:

use a travelplanner-not the app/this site, but best is bahn.com.(german railways) It covers nearly all of EUR ad is frequently updated-this app not.

Start with A to B and see what it delivers=the general route -you have to change trains a few times-via PL-CZ or SK-HU.

Now think which places you would like to visit on the way and divide up in these segments-more trains/connections will appear. Do not too far advance-mostly it is till 2 month later possible-it will give general idea of what is available.

You may already note that from LT to PL-ONLY in summer-ONY on sat/sun, there is just 1 train Kaunas-Suwalki-on to Bialystok/PL. This is PolRegio-moist fast trains in Pl are done by PK_these MUST be REServed-I have no idea what LitRail can do for you.

Check LitRail-if you will use pass-what the procedure is-there are various reports about this lately.

When you pass PL daytime trains do not really need to RES onard-till in HUngary.

It depends on where in RO-there are several routes-several trains -and several other connections-the long distance trains MUST be REServed again, best whilst in BudaPest-or maybe advance via site of mav.hu. Cost for REServ is extra to pass-but in these areas its only a few € extra.

This site is about railpasses-depending on your age, if you want to visit more places, willing to go out of your way and fix bookings-but maybe a pass may not be best buy-most of the railways here give generous discounts and have low fares anyway to start with.

Now first do the homework and come back if you hit other problems

Thank you