[name_m]Welcome[/name_m] to Nameberry!
[name_f][/name_f]I think [name_m]Donovan[/name_m] and [name_m]Elijah[/name_m] both work well with your set while tapping into different aspects of your blended sibling set. Not sure if popularity is a factor in your decision making, but [name_m]Elijah[/name_m] is currently much more popular in the US than [name_m]Donovan[/name_m] (though so is your T’s name). I like alliteration, but I agree [name_m]River[/name_m] is too much. I think [name_m]Rafael[/name_m] works, though!
[name_f][/name_f]Other suggestions (avoiding -er, long “i” sounds, and another A beginning):
[name_f][/name_f][name_m]Dashiell[/name_m]
[name_f][/name_f][name_m]Declan[/name_m]
[name_f][/name_f][name_m]Cormac[/name_m]
[name_f][/name_f][name_m]Vincent[/name_m]
[name_f][/name_f][name_m]Zane[/name_m]
[name_f][/name_f][name_m]Kieran[/name_m]
[name_f][/name_f][name_m]Nico[/name_m]
[name_f][/name_f][name_m]Jonah[/name_m]
[name_f][/name_f][name_m]Nathaniel[/name_m]
[name_f][/name_f][name_m]Gabriel[/name_m]
[name_f][/name_f][name_m]Caleb[/name_m]
[name_f][/name_f][name_m]Ezra[/name_m]
[name_f][/name_f][name_m]Ezekiel[/name_m]
[name_f][/name_f][name_f]Sage[/name_f]
[name_f][/name_f][name_m]Forest[/name_m]
[name_f][/name_f][name_m]Blake[/name_m]
[name_f][/name_f][name_m]Chase[/name_m]
[name_f][/name_f][name_m]Dylan[/name_m]
[name_f][/name_f][name_m]Logan[/name_m]
[name_f][/name_f][name_m]Evan[/name_m]
[name_f][/name_f][name_m]Julian[/name_m]
[name_f][/name_f][name_m]Damian[/name_m]
[name_f][/name_f][name_m]Henry[/name_m]
[name_f][/name_f][name_m]Owen[/name_m]
[name_f][/name_f][name_m]Leo[/name_m]
[name_f][/name_f][name_m]Sebastian[/name_m]
[name_f][/name_f][name_m]Felix[/name_m]
[name_f][/name_f][name_m]Jude[/name_m]
[name_f][/name_f][name_m]Benjamin[/name_m]
[name_f][/name_f][name_m]Samuel[/name_m]
[name_f][/name_f][name_m]Lucas[/name_m]
[name_f][/name_f][name_m]Edward[/name_m]
[name_f][/name_f][name_m]Dante[/name_m]
[name_f][/name_f][name_m]Reuben[/name_m]
[name_f][/name_f][name_m]Florian[/name_m]
[name_f][/name_f][name_m]Tobias[/name_m] (has a long “i” but I think it works + another T!)