Todiste ja tosite ovat selvityksen mukana.

Because the subject is todiste ja tosite — two separate things joined by ja (and). In Finnish, that makes the subject grammatically plural, so the verb is plural too.

• on = is
• ovat = are

So even though each noun is singular by itself, together they require ovat.

Because the sentence refers to one proof/evidence item and one voucher/receipt/document. Finnish does not automatically make the nouns plural just because there are two nouns joined by ja.

So the pattern is:

• todiste = one proof
• tosite = one voucher/document
• todiste ja tosite ovat = a proof and a voucher are

This is the same idea as in English: the book and the pen are here. Each noun is singular, but together they form a plural subject.

They look very similar, but they are not the same word.

• todiste usually means proof, evidence, something that shows a claim is true
• tosite usually means a supporting document, receipt, voucher, or other document that verifies something, especially in administrative or accounting contexts

So a learner should not treat them as interchangeable, even though they are close in form.

Selvityksen is the genitive singular of selvitys.

• basic form: selvitys
• genitive: selvityksen

The -n ending is the normal genitive marker in Finnish.

In this sentence, the genitive is used because mukana commonly appears with a noun in the genitive:

• X:n mukana = with X, accompanying X, included with X

So selvityksen mukana means something like with the report/explanation/account.

Here mukana means along with, accompanying, or included with.

In the structure genitive + mukana, it often means that something comes together with something else:

• kirjeen mukana = with the letter
• paketin mukana = with the package
• selvityksen mukana = with the report/explanation

So in this sentence, mukana does not mean simple physical togetherness only. It has the very natural sense of being enclosed, attached, or included with something.

This is a very common confusion.

• mukana usually expresses a state: being along, included, present with something
• mukaan often expresses direction or has meanings like along, into the company of, or according to

Compare:

• Todiste on selvityksen mukana.
  The proof is included with the report.

• Otin todisteen mukaan.
  I took the proof along.

• Selvityksen mukaan...
  According to the report...

So in your sentence, mukana is correct because the sentence describes a situation/state, not movement.

Usually not if you want the same natural meaning.

• kanssa means with in the sense of together with
• mukana often means included with, accompanying, coming along with

For documents, attachments, enclosed items, and similar contexts, mukana is much more idiomatic.

So:

• selvityksen mukana = natural for included with the report
• selvityksen kanssa = possible in some contexts, but it usually does not sound as precise or as natural here

No. Finnish word order is fairly flexible, although the given order is neutral and natural.

The sentence as written:

• Todiste ja tosite ovat selvityksen mukana.

This is a normal, straightforward order:

• subject
• verb
• adverbial phrase

You could also say:

• Selvityksen mukana ovat todiste ja tosite.

That version puts more focus on selvityksen mukana.

So the basic meaning stays the same, but the emphasis can change.

Because Finnish does not have articles like English a/an and the.

That means todiste, tosite, and selvityksen do not by themselves tell you whether English should use:

• a
• the
• sometimes no article at all

The exact English article depends on context. Finnish leaves that information to the situation, previous mention, and overall context.

Yes. They are common Finnish -e nouns, and their forms change in a way learners should notice.

For example:

• todiste → todisteen → todisteet
• tosite → tositteen → tositteet

So although the basic form ends in -e, other forms often show -ee- or -te- / -tte- patterns.

This matters because these two words are easy to confuse both in meaning and in inflection.