Dependent visa

Hello everyone,
I am a nurse working in nhs and I came to UK around a year and half now .I am divorced and I have a small child 4 years.when I first came to UK under tier2 visa I didn't bring my son because I had to do some exam to secure my job and visa so after 3 months after I pass my exam.I decided to wait because I thought the city I was working in wasn't a suitable place to live with my son and I was concerned about my child care options .So I changed my employer and due to employment process and Covid and home office stop working during the first lockdown.I did my application in June and I got my decision in October and I realized their was a mistake in my decision so I request admin review which luckily was successful in December and I am yet to receive my brp.
I did finally received my email from TNT and they said they will deliver it Tomorrow.
My question is I am planning to apply for my son the minute I receive my BRP .I do have a paper from court saying I have custody for my child not full custody just the word custody.and my parents was taking care of him meanwhile I was working .so Do I need a lawyer to help me with application to avoid refusal
Especially that I took so long to apply for him.or do I apply for him my self and take my chances
I did ask a lawyer and he ask for 800 pound to do the application which seem alot for me. the child father is alright with me taking the child to UK.and he lives in the same city as my parents.
Sorry again for the long post. But what you people think should I go for a lawyer and pay that money or try by myself.

Thank you

You need to prove sole responsibility to bring the child. See link below.

immigration-for-family-members/sole-res ... 13087.html

So you think better a professional help