The current nursery is wrong. You must be in England because you mention EHCP, so the ratio in a mainstream nursery for children aged 3+ is 1:8 or, if there is a qualified teacher or someone with one of the other approved level 6 qualifications, 1:13. See here.
If an ECHNA has been requested, what week are you on?
Once an EHCNA has been requested, the LA has 6 weeks to inform you if they will agree to assess or not. While you can state your case and send evidence, it will be the LA making the decision. If they refuse to assess, you should appeal. If they agree to assess, they will proceed with the Needs Assessment.
As part of the EHCNA, the LA must seek advice and information from:
a) the child’s parent or the young person;
b) educational advice (usually from the head teacher or principal);
c) medical advice and information from a health care professional;
d) psychological advice and information from an educational psychologist;
e) advice and information in relation to social care;
f) advice and information from any other person the local authority thinks appropriate;
g) where the child or young person is in or beyond year 9, advice and information in relation to provision to assist the child or young person in preparation for adulthood and independent living; and
h) advice and information from any person the child’s parent or young person reasonably requests that the local authority seek advice from.
You will be involved in giving your views, etc. but, again, you won’t be involved in the actual decision about whether to issue or not. If they refuse to issue, you should appeal.
If the LA agrees to issue, the LA doesn’t need your agreement to finalise. They can do that even if you disagree with the content of the EHCP. If you disagreed, you would then have to appeal.
An EHCP is not the same as an ICP.