Which part of speech is 'together' in the sentence?

Yes, an adverb. 'Simultaneously' sounds a little bit too 'together'! 'In union' is wrong and I don't think it is natural English. 'At the same time' is OK. In any case, you should make it clear that they also come of the same mother, I suppose.

A dictionary has this: Septuplets are seven children born at one birth.

All your suggestions are wrong, I'm afraid.

You need '. . . at the same birth', as they always emerge one after another, not together.

('...simultaneously' makes my eyes water just thinking about it.)

Hi Mister Micawber,
Thank you so much for your reply and phrase.

Best,
TS

Rover_KE('...simultaneously' makes my eyes water just thinking about it.)

Hi Rover,
Thank you for your reply and phrase. I did it. That's why I said 'They don't sound very well to me'.

Best,
TS

hello teachers,

I have a difficulty in naming what are the parts of speech this is the paragraph the ones in bold are the words I need to say what type of part of speech they are

the paragraph:

They want governments and the world’s best scientists, technicians and engineers to work together to create new inexpensive technologies that produce large

Adverb modifying born “how”