A lot of bugs and Annoyances. Example, Everytime a player joins the realm gets more laggy

I made a realm about a week now and I tried posting about my problems on the Minecraft forum and they recommended me to try it here. One of the many problems I'm facing revolves around players getting laggier whenever a new member joins. For example, 1-2 people would be fine but when a third person gets on the server gets really laggy and sluggish. I do not have bad internet either as I'm getting 117.7 Mbps. Another problem I am facing in my realm is a render distance problem. Everyone is set to the default lowest possible setting of the render distance and I try to reset the realm and upload a copy with a higher render distance, but the effort goes futile as it just resets back the lowest setting. The third and final problem I have with the server is a tick delay during Redstone contraptions.