Fourteen Bonded Brothers - maybe more!

Question

To start the riddle
We are fourteen brothers
There might be more of us
But we haven't found the others

Our first brother isn't metallic
But he has visited the stars
Our second swims very well
And drives electric cars

The third of us lived in your stationery
Yet he can be much more precious
Our fourth brother is rather bright
Also, he's the least moodiest

Our fifth brother always carries a lamp
And he helps plants grow
Our sixth likes going to Norway and Sweden
Or Denmark? I don't know.

Next, our seventh is a man of steel
Twentieth dollar? That's easy
The eight brother is similar with our fourth
Yet he really likes photography

You barely can meet our shy ninth brother
Well maybe, he's the richest of all
Our tenth brother thinks he's Roman
And also, he's the most punctual

Our twelfth brother sells jewellery
Naturally, he gets lots of attention
Our last brother only lives for a day
A city in Russia he often mention

Realize two of us are missing?
Well, we know them very little
It's your job to find out their names
And therefore, you've solved the riddle!

Hint:

These guys follows two things.

Answer 1

The brothers are

the elements whose atomic numbers are triangular numbers: $\frac{n(n+1)}2$.

First brother:

Hydrogen which is not metallic, and is found in stars.

Second brother:

Lithium which floats on water and is used to make rechargeable batteries.

Third brother:

Carbon can be in the form of graphite, which is in pencils, and diamond, which is much more precious.

Fourth brother:

Neon gives off light and is the least reactive?

Fifth brother:

Phosphorus is used to light matches and lamps and is used in fertilisers.

Sixth brother:

Scandium. Scandinavia = Denmark + Norway + Sweden.

Seventh Brother:

Nickel is used to make stainless steel. Twenty nickels make a dollar.

Eighth brother:

Krypton is also a noble gas and is used in photography lighting (Thanks @jdow)

Ninth Brother:

Rhodium is rare and the most expensive of all precious metals.

Tenth Brother:

Caesium. Julius Caesar was Roman. Caesium radiation is used to define a second of time.

Twelfth brother

Platinum is used to make jewellery and is used to refer to famous albums (Thanks x 2, @jdow!)

Last Brother

Dubnium has a half-life of just over a day and is named after Dubna, a town in Moscow Oblast, Russia.

The two missing

Eleventh brother:

Dysprosium

Thirteenth brother:

Protactinium

I don't understand the two clues in brackets...