Dear Querist, in relation to your query my opinion is as follows:-
1. No need to file a partition suit in your case, as there is an already existing written settlement.
2. First and foremost file an injunction suit and ask for mandatory injunction to handover the keys of your house to you and permanent injunction can be sought where you will ask the court to permanently restrain your brother to enter your house.
3. Any suit which is seeking the relief of possession or partition, you have to pay a hefty court fee, and in your case it is not required.
4. In case you opt for partition suit, then you have to ask partition in the whole suit property and have to pay court fee According to your share in the whole suit property.
5. You can very well ask for your share in the suit property even if your mother is still alive as the whole property was in your father's name and when he died without a will, you all became legal heirs and the whole property can be divided as per your wishes.
6. In case of a declaration suit, you always ask the court to declare something, in your case ultimately by filing a declaratory suit you are seeking partition, so you have to pay the court fee in that case as well. And there is no need for seeking declaration or partition.
Hopefully, the first two points will satisfy your requirements, in case of any further query, feel free to call.