There are many things which can cause a computer to run slower. But since this computer originally ran much better I don't believe the first solution to try would be adding a new SSD.
Once you have posted the Speccy we will be able to see what RAM was added. If the added module is slower than original modules the original RAM will underclock to the speed of the slower module.
Since this is a "family" computer this opens the possibility that third party software may have inadvertently been installed when downloading and installing programs online. The author of the software can generate more revenue by allowing third party software to be bundled with their own software. These third party applications can contain anything from toolbars, potentially unwanted software, even adware. The third party software can usually be avoided by using the custom installation options. This allows you to see every application being offered so that you will have the option to decline the applications you don't want it.
The program I'm going to suggest you run is considered to be a security scan, a tool usually relegated to the security forums. But it does find PUPs (potentially unwanted programs) such as the third party applications I mentioned previously.
Please run AdwCleaner
When AdwCleaner opens you will see an image like the one below.
Click on Scan to start the scan.
Once the search is complete a list of the pending items will be displayed. If you see any which you do not want removed, remove the check mark next to it.
If there are no malicious programs are found you will receive the following message.
Click on Clean to remove the selected items. If you have any questions about any items in the list please copy and paste the list in your topic so we can review it.
You will receive a message telling you that all programs will be closed so that the infections can be removed. Click on OK. The computer will be restarted to complete the cleaning process.
When the cleaning process is complete a log of what was removed will be presented. Please copy and the paste this log in your topic.
Periodic maintenance becomes important with different users. Regular defragmenting the hdd, using the disk cleanup tool, clearing the temp file folder, and the list goes on.