AWS RDS MySQL limit connection

We have multiple databases in a single RDS instance. Because of any reason if we have load in 1 database it stops all the databases. I'm not able to move any of the database because of following reasons: 1. In MySQL triggers we are calling other databases and as they are in a same server it works. 2. What we can written in trigger we can write the same in App Server but it's going to be tedious tasks. 3. I'm not using Aurora so Lambda functions are out of scope for me. So, currently I'm looking for a solution where I can limit the database so even if there were too much db load it should not bring down all the databases. AWS RDS MySQL5.7 Thank you in advance.