The reliable way to hire a tradesperson

hi, we've been having issues with our architect and are thinking we might be better taking on stage 5 riba without them. we are doing a ground floor extension with some changes to internal walls/bathrooms. we have gotten to the stage where we have tender documents now and have been trying to understand the regulations on line with respect to getting sign off from a principle designer as part of building completion. some sites say that an experienced builder can provide this, others say that it needs to be someone specifically qualified. im not really sure if we end up parting way with this architect if we will end up needing to pay out for a new architect to take over and provide that sign off. also, i'm not sure if the expectation would be that the building company could/should continue conversations with structural engineer/building control/party wall surveyor or if we'd have to do that. sorry if the questions are a bit haphazard or dont make sense! new to this all. i'm also not sure if i'm thinking about/asking the right questions or if there are other things i should also be asking or considering! thank you very much for any advice and suggestions in advance!

We will be moving into a property next month with artificial grass in both front and rear gardens. We will be looking into hiring to remove this and replace with grass instead as we prefer real grass. What would a job like this entail? We're keen to understand the process as we have a dog and a toddler so want to ensure any disruption we can plan for / have them out the way if necessary.,

Had a loft wetroom fitted. Before getting to use the shower I noticed the grout had come out and tiles were moving. The room was impey tanked but I think the floor boards were only nailed down. As the rest of the loft I had to go around and screw all the boards down before the carpets went down. Is there anyway I can take the tiles up and the impey membrane and reinforce the subase? Without having to remove the wall tiles? It's cost me a small fortune so far but it's just a waste of space at the minute.