Euss family permit

Hello!

I am a EU national with pre-settled status living and working in UK for 3 years.
My partner and I have been living together for the last two years. We have bank statements in joint names.
My partner thought has not a legal status.
We have been given our notice of marriage but due to Covid our marriage has been scheduled late May from the council.
My lawyer is advising my partner to apply for Euss as unmarried partners and when we get married we submit our marriage certificate.

I would like a second opinion and advice please.
What is the best option for us?

Thank you