That is one beautiful knife and to have the family history and the sheath is great. I thought from the style and markings that it is one of the Bowie style hunting knives post 1891(marked England) but there are many variations. Post it on Bernard Levine's forum. (link I listed) He wrote the book Levine's Guide to Knives. There is a section on these in his book.
I would like to see what Mr Levine says about the silver handled one. It might be a user but might be worth more than you think. I am perplexed by the silver handeled Bowies.
That is interesting about snaps being invented so early.
Do you have a reference to dating the Ltd mark on the I*XL? I have not seen this and would be interested on seeing pics of all the variations of Wostenholm marks.