Child support and his family and his work

Atty, I need your advice. I want to file a petition for child support from my husband kasi he left us for another woman. Nakilala niya yung kabit niya sa work nya (seaman). Before he was giving 10k a month for support pero ngayon wala na since last year. I want to file this also sa company nila sana (his parents are running the manning agency.) They should know how much should be given to me pero wala. Alam ko kasi may mandatory yung dependents na percentage sa allotment. Ngayon, gusto ko meron nang galing sa batas na kailangan nyang magbigay samen ng anak ko.

Pero hindi ko alam kung anong una kong gagawin. Demand letter lang ba? file a petition for child support? And saan ako pupunta? Kailangan ba ng lawyer agad para dito? Please let me know. Thank you.