Requesting for my and sons passport to be return

[Crissy]

Good evening everyone

I need some advice here as I'm very confused.
My partner is about to sent a visa application under 10 yr route. We've missed his renewal date which was meant on may 6 2017 due to financial difficulties . But we have gathered the complete funds now and we are ready for application. I understand that he needs to make a new application and that he needs to restart the 10 yr route. However me and my son is travelling next month back to our own country for one month.
We spoke with our solicitor and he said we have two options:
1) send the application without mine and sons passport.
2) send the application and request for our passports back. He said it will be back within 14 days.

After searching online I found out that requesting for documents back I'll cancel the application. Is that true? And is it really possible to get our passports back within 2 weeks because I don't want to take a risk.
Apologies for the long write up
Your replies is highly appriciated.
Thank you.