My situation: I had two agents request full manuscripts of my first YA Novel. Agent One said sheʼd like to see a revision and named specific issues to address. Agent Two said the writing was strong but he did not connect with the manuscript enough to offer representation but would like to see more of my work. Both are well-respected agents at top agencies. I could envision working with either of them. Iʼve completed the revision of my first novel and my second novel is also ready for submission. My question: Is it okay to send Agent One the revision and Agent Two the new novel simultaneously?Yes.
And, should I keep sending queries to other agents after Iʼve submitted to either of the above two agents?Yes.
The thing you don't do is send the revision based on Agent 1's comments to anyone else until Agent 1 has looked at it and/or had at least a couple months to respond. You can keep on sending the original of the manuscript to other people, but once you've taken someone's creative input and decided it makes the manuscript better, it's respectful to give that person the first shot at the results of their good advice.