Are they behind???????

my brothers are 2 and 8 months. we think they may be behind in the speaking area. The know a lot of words. they cannot put them in sentances tho. and they cant pernunciate most constinants (letters that arent vowels) like if they want a cookie they go to the cabinet and say (ooee) or if they want to use the potty they go to the bathroom and say (ahh eee) and I am there sister and my name is bailey but they call me (ayay) but they can say "my shoe" or "charlie's shirt" but it sounds like (my ooh) or (Arees urt) they are SUPER smart but cant show it. what should we do!!!!!!!!!!!!!