No, these sentences do not make sense...🤔 What do you mean by "big bother"? What do you mean by HOH? What do you mean by "allies" in this context? What do you want to save your girlfriend from? "to" and "so that" can (not "always") have similar meanings, but slightly different constructions: - I need to work hard to improve my English. - I need to work hard so that I can improve my English. also: - I need to work hard in order to improve my English.

Yes, both work, but I'd use "safe" and not "saved". Unless "saved" has a specific technical meaning on Big Brother; I don't watch the show. I need to win this HOH to keep my allies and my girlfriend safe. "To" works. I need to win this HOH so that I can keep my allies and my girlfriend safe. "So that I can" works, not just "so that".

SO THAT — PURPOSE An action/plan may be followed by so that + a clause that expresses purpose or goal. The clause after so usually includes a modal, such as can, could, will, would, may or might, all of which express general timing. The time of the purpose is usually (but not always) later than the time when one makes the plan. A similar meaning can be expressed with in order + infinitive clause. We decided to stay out all night so that we could¹ watch a meteor storm. (connective preposition + that-clause) SO — RESULT An action or a situation may also be followed by so + a clause that expresses result (effect). A past tense cause-effect clause requires more precise timing. For this reason, (be) able is used instead of could when expressing ability. A somewhat similar meaning can be expressed with the intensifier so in the main clause followed by that + result clause. We stayed out all night, so we were able² to see the meteor storm pass. (PP) Hope you got this! (coordinator "result") We have lots of blankets, so we will be able to keep ourselves warm.