Can I take it your Fiancée and child have British Passports ?
And that you have a Filipino passport ?

If this is the case, then without a confirmed offer of employment from a licensed sponsor employer you'll need to follow the usual UK immigration rules for partners.

Based on the information you've shared, the major issue will be meeting the Financial Requirement.
This means your sponsor (partner) will need to have a minimum annual gross income of £18600 plus adequate accommodation. This applies to both Fiancé and Spouse.
The advantage of being married at the time of visa application is that upon arrival into UK you would be eligible for employment right away. Under Fiancé visa no employment is allowed until you are married and have applied for and been granted a visa for Further Leave to Remain.