I'm sorry to say it so bluntly, but in my opinion, it also doesn't make sense to try to "save" this floor plan. Many things are just not right. Therefore, it will be much easier for a trained architect to plan something new from scratch than to try to improve it.
May I ask why you would like to have the bedroom on the ground floor [EG]? The background of my question: In my opinion, it would be more advantageous and sensible to swap the bedroom and office. The upper floor [OG] should be planned in such a way that the bathroom is accessible from the office/bedroom and the children's room without having to walk through the respective other room. On the ground floor [EG], you could save space and, of course, also costs for the bathroom. Or, if you want to keep the option open in old age to have everything necessary on the ground floor [EG] without having to climb stairs, you could plan a shower bathroom on the ground floor [EG] and dispense with a toilet there. The office could then be planned on the ground floor [EG] in such a way that it can be easily converted into a bedroom later in life. But as it stands, I think having 2 bathrooms plus a guest toilet is just too much considering the available space and budget.