A grelha e a pinça estão limpas.

Because the subject is compound: a grelha e a pinça = two things joined by e (and).

In Portuguese, a compound subject normally takes a plural verb:

• A grelha está limpa. = one item
• A pinça está limpa. = one item
• A grelha e a pinça estão limpas. = two items

So estão is the 3rd person plural form of estar.

Portuguese adjectives usually agree with the noun they describe in gender and number.

Here, both nouns are feminine singular:

• a grelha
• a pinça

Together, they form a feminine plural subject, so the adjective becomes feminine plural too:

• singular feminine: limpa
• plural feminine: limpas

That is why the sentence ends with limpas.

Because both nouns are feminine.

When all nouns in the group are feminine, the adjective stays feminine plural:

• A mesa e a cadeira estão limpas.
• A grelha e a pinça estão limpas.

If there were a mixed-gender group, Portuguese normally uses the masculine plural:

• O prato e a xícara estão limpos.

So in your sentence, limpas is the correct form.

Because clean in this sentence is treated as a condition/state, not a permanent characteristic.

Portuguese often uses:

• estar for states, conditions, results
• ser for identity, essential characteristics, definitions

So:

• A grelha e a pinça estão limpas. = They are clean right now.
• A grelha é limpa. = The grill is clean / easy to keep clean / generally clean in nature

In everyday situations like talking about dishes, tools, kitchen items, or things that have just been washed, estar limpo/a is the natural choice.

In Portuguese, it is very common to repeat the definite article before each noun in a list or pair:

• a grelha e a pinça
• o prato e o copo
• a faca e a colher

This sounds natural and standard.

You may sometimes see the article omitted before the second noun in some contexts, but repeating it is very common and often clearer, especially for learners.

Yes.

You can tell from the article a:

• a grelha
• a pinça

That means each noun is grammatically feminine, which is why the adjective ends up as limpas in the plural.

Their singular forms with the adjective would be:

• A grelha está limpa.
• A pinça está limpa.

A rough Brazilian Portuguese pronunciation guide:

• grelha: GRE-lya
  The lh sound is like the lli in million for many English speakers, though not exactly the same.
• pinça: PEEN-sa or PIN-sa depending on accent and how detailed you want to be
  The ç is pronounced like s

A few useful sound notes:

• lh is a very common Portuguese sound: filho, mulher, alho
• ç always sounds like s: cabeça, açúcar, pinça

Grammatically, it is possible, but it usually changes the nuance and often sounds less natural in this context.

• estão limpas = they are clean now; their current condition
• são limpas = they are clean by nature / generally clean / usually clean

For objects that have been washed or are in a clean state at the moment, estão limpas is the normal choice.

In standard Portuguese, when a group includes at least one masculine noun, the adjective usually goes in the masculine plural.

For example:

• O garfo e a faca estão limpos.

Even though faca is feminine, the presence of garfo makes the adjective default to limpos.

But in your sentence, both nouns are feminine, so limpas is correct.

Yes, but the normal, neutral order is the one you have:

• A grelha e a pinça estão limpas.

You could also say:

• Estão limpas a grelha e a pinça.

This is grammatically possible, but it sounds more marked or stylistic. For a learner, the original order is the best one to use.

Yes. Each noun by itself would use the singular:

• A grelha está limpa.
• A pinça está limpa.

When you combine them with e, both the verb and adjective move to the plural:

• está limpa → singular
• estão limpas → plural

This is a very common Portuguese agreement pattern, so this sentence is a good model to remember.