Hi Michaeliu,

The short answer is sure, you can use the conjunction "and" to connect those two parts of the sentence.

The longer answer is that your example breaks the rule of parallelism, by which I mean that "whose parents are out of town and his grandparents are staying with him" is incorrect in its construction. "Whose parents..." needs "and whose grandparents" to show correct parallel structure.

Good on your for discovering FUNBOYS. Those little conjunctions are used to connect two independent clauses. I would not go so far as to say it is INCORRECT to use a comma when joining two independent clauses, at least not always.

Be careful to use a comma when a little conjunction joins two independent clauses, UNLESS the conjunction is - as in your example - a subordinating conjunction. Let's look at your example with the word "because" in the place of "for," to make it obvious:

I'm late for school because the traffic jam was so bad this morning. CORRECT. NO COMMA.

In this example, "because" is a subordinating conjunction and you do not need a comma. In fact, adding a comma would be incorrect.

But let's look at a different example with two independent clauses:

I'm late for school this morning, and I did not have a chance to eat breakfast.

You might argue that, stylistically, it is simpler to omit the comma, and you would be correct. But, grammatically, it is correct to use a comma when joining independent clauses. It is very necessary to use commas when joining more than two independent clauses. Here is an example:

I'm late for school this morning, my hair is a complete mess, and I did not have a chance to eat breakfast.

You can see that the three independent clauses need to be separated by commas, and the final independent clause needs the little conjunction "and."

My point is to be careful which conjunction you apply the "no comma" rule to.