Hi moh, and welcome to MySwissAlps!
>> I am planning to come Switzerland via train from london what would the best way to get there
There are several routes. You can use the Swiss Timetable to plan your route from London to Switzerland:
>> and does swiss pass allow us to use the international train?
No, you will need separate tickets for your trip from London to the Swiss border.
>> I saw on rail Europe a grand tour of Switzerland in 4 days.Would you recommend this?
No, I'm afraid wouldn't. It's far too rushed, even unrealistic, and involves long travel times every day. You can use the Swiss Timetable to check travel times yourself for that suggested itinerary.
For a 4-day trip, I would suggest you stay in one place only, either Luzern or in the Jungfrau Region (Interlaken, Lauterbrunnen, Grindelwald, Wengen or Mürren).
>> Also how easy is it to find cheap hotels for a night on that tour or at the hotels included?
What they are selling on that page is just a Swiss Travel Pass. How easy it is to find cheap hotels depends on the time of year and how far ahead you book (and what you mean by "cheap"). When you have decided where you are going, this page can help with finding accommodation:
I hope this helps.