Had the same speech issue with my first born.
Talked to a speech therapist in an elementary school in MS.
She said: take into consideration that boys mature slower than girls and that includes speech. She gave me a list of phonetics in the (generally accepted) order of learning and some sounds aren’t completely conquered until 6 … especially for boys.
Pre-school is like a jumping board. The first month fixes almost all the concerns you may have with a child’s speech. (Teachers are trained to hear possible problems and will bring them to you – if she doesn’t, get a new teacher.)Then the first born teaches the second and you no longer have concerns about them learning how to speak.
The concerns later revolve around teaching them how to shut up.