Worried about milestones

My 15.5 month old is lagging a bit compared to his half-siblings. While he can say “mama” all the time, he only sometimes says “dada.” He sometimes calls the dog “dah” and everything else is “cah” (we have two cats). He has also started saying “ball” (usually “bah”) and “hi”. He will shake his head “no” but hasn’t used the word yet. And then when it comes to walking, it seems like he’s struggling. He cruises constantly and will push himself around using a walker when it’s around (we got rid of ours at home because we worried it was hindering his ability to walk independently) but he can only take 3-5 steps unassisted. Any advice?