Greetings from Tatiana!
Matfei is pronounced just like you see it, pretty easy, M-aa-t-f-ei,
the other version, Matvei.
I am sorry, but what does Krotyss mean? Is it from Krot, which is mole?
If I know what you are trying to accomplish, it would be easier to
help form the name.
Sofya is right, double SS is not typically Russian, probably just a
latinisation, done to emphasize the S at the end of the word.
As far as I know, two bynames were not common, if used at all, in
medieval Russia (correct me if I am wrong), but you can use a patronim
and then a byname.
Best of luck,
> I have the given name Matfei (Matthew) but would like to know how that
> is actually pronounced.
> Then we have the byname Krotyss.
> What I wanted to know was if it would be possible to use two bynames
> or a byname and a toponym and if the latter is feasible, what order
> should they come in?