> Are the lineups of both sides submitted without knowledge of the opposing lineup?

Though I cannot confirm, I'd imagine so. Otherwise, there is a possibility of tampering with the lineups to gain competitive advantages. The following quote (also found below) alludes to strategy being used when a team sets their lineup, and the captains only have knowledge of the other's lineup after the lineups are submitted when they are announced (if not shortly before announcement). 

> Do you send out your strongest
> players first? Or hold them off in anticipation of The Ryder Cup
> coming down to one of the final matches? Captain Bjørn and Captain
> Furyk will assess the scoreboard, and their team, before setting the
> order in which their 12 players will be sent out. After cementing
> their respective line-ups, the captains will reveal who will face-off
> in the final session of The 2018 Ryder Cup.

----------

> If not, which team submits its lineup first?

According to the [Ryder Cup themselves](https://www.rydercup.com/news-media/europe/when-are-pairings-announced-ryder-cup), the captains have a window of time to submit their lineups. It is not clear whether one team is required to submit their lineup before the other team, but a team is required to submit their lineup before a specified time.

Below are the deadlines for submitting pairings during the 2018 Ryder Cup:

> **Friday, September 28**
> 
> **12:35- 13:05:** Afternoon pairings submitted - As the opening session
> draws to a close, both Captain Bjørn and Captain Furyk will have a
> short window of time to make any necessary adjustments before they set
> their line-up for the afternoon foursomes matches, which is an
> alternate-shot format.
> 
> **One hour after play:** Saturday morning pairings submitted: Following
> the conclusion of Day One, both captains will have time to consult
> with their Vice-Captains and their players before they are required to
> submit the pairings for Saturday morning’s fourball matches no more
> than one hour after the second session is completed.
> 
> **Saturday, September 29**
> 
> **12:35- 13:05:** Afternoon pairings submitted - With the point totals
> beginning to add up, each captain will have a better sense of how his
> players are faring, and the submission of Saturday afternoon’s
> foursome pairings offer Captain Bjørn one final chance to send out the
> strongest two-man teams, as well as rest key players before all 12
> compete in the Sunday singles matches.
> 
> **One hour after play:** Decision time. Do you send out your strongest
> players first? Or hold them off in anticipation of The Ryder Cup
> coming down to one of the final matches? Captain Bjørn and Captain
> Furyk will assess the scoreboard, and their team, before setting the
> order in which their 12 players will be sent out. After cementing
> their respective line-ups, the captains will reveal who will face-off
> in the final session of The 2018 Ryder Cup.

----------

> Can the lineups be modified once submitted?

I'd imagine not. The following quote (also found above) alludes that lineups are final.

> After **cementing** their respective line-ups, the captains will reveal who will face-off in the final session of The 2018 Ryder Cup.