You are filling out a Standard Visitor Visa application and have arrived at the part where they are making first-level enquiries about your visit. You have listed out a few such questions and ask what how they are different, presumably you want to know how to answer them.
Background. Those questions have been on the application form for at least 20 years or so. Over that period of time, they have been hammered and honed polished by the Home Office in both public and invited consultations with the UK legal community. It means everybody with something worthwhile to say about it on both sides of the fence has had input.
It also means there are no unfair questions and no ambiguous questions and more importantly for a lot of people, there are no "trick questions". There is guidance to go along with the questions that has also been hammered out in consultations and people who are "on your side" have had input to what is presented to the end user. In my experience they stopped doing 'whimsical' or disingenuous refusals as a matter of policy in 2006 and they invented the Chief Inspector in 2007 to keep an eye on things.
Let's look at your question...
can someone please help differentiate the 4 question and what they
What they "really mean" is inherent in the natural meaning of the words as an English-speaking person with basic education would understand them.
The "best practices" approach is to take the questions at face value and answer them accordingly. The ones you have listed in your question ask for a single number where you can use their own reference at OANDA to convert your local numbers. If you do not know the answers, then you should seriously consider whether or not making an application is appropriate for you at this point in time.
Honestly, these are not 'hard' questions, put the numbers down and then sync up your evidence so that the numbers are supported. Your English usage on this site informs us that you are at an advanced level and capable of understanding the questions without difficulty.
If, on the other hand, you are having trouble, the 'best practices' approach is to instruct a solicitor with a solid practice area in representing applicants who have a valid premise but are in reduced circumstances. A representative example would be a solicitor like Sonu Vijh, who built up a practice on Commercial Road near Tower Hamlets. Paradoxically, they attract a fee and you won't get anywhere without paying. It's pointless to try and get free information from them because they already worked on hammering out the UKVI application form and the guidance brochure. In your case I would guess the fee would be about GBP 800, but that's strictly a GUESS. Maybe more, maybe less. They can get in to serious trouble for taking casework where there's no hope of success.
You can use the Law Society's search facility to find a solicitor who speaks your mother language.
Just to repeat, I don't think the step of instructing a solicitor is necessary given your level of English comprehension, but it's out there if you want to pay for it.
Infants and children under 18 who are making an application under the supervision of an accompanying parent can put "N/A" and reference the primary's GWF number in the remarks section. They DO NOT have to submit copies of the primary's evidence. ECO's are not idiots and already understand that infants and children under 18 do not have the capacity to answer those questions.
The current visitor rules are in Appendix V of the Immigration Rules.
The guidance is at "Guidance on applying for UK visa to visit or for short-term stay"
The Solicitors Regulation Authority enforces the rules for practising solicitors as laid down in the Legal Services Act 2007.
The Law Society is the UK's official designated body for establishing who is qualified to be a solicitor.
The Commissioner promulgates a code of practice in accordance with the Immigration and Asylum Act 1999.
The Chief Inspector was established by the UK Borders Act 2007. My personal view is that he's pretty good and reading his reports is time well spent. Every year he broadcasts an email to the UK legal community asking if there's any irregularities he should be looking at, and then he follows up on it with the full force of his office. He's cool. He is in the "good guys club".
Disclaimer: I have known the mentioned solicitor for about 15 years and mention her explicitly only as an example that such people are out there (it's posted without her permission or knowledge). There are several of them. It is a violation of UK law and the Commissioner's Code to receive compensation or recognition for a referral in the first instance.
Some of the application questions you have listed are part of a sequence and and need to be examined as a stream. Accordingly, some have been taken out of context.