TP-Link WR841N, that is a pretty old N300 with only 10/100 speed ports, I can see it having some problems handling a lot of clients. The Belkin AC900 DB *should* be better since it has gigabit ports and AC900, but after reading reviews there are better choices.
Personally I have had really good luck with TP-Link's AC models, the
TP-Link C1200 is a very good basic router with gigabit and AC1200 capability and is currently on sale for $40 so it's a very good budget choice. The
Archer A7, as well as the older model the
Archer C7, is only slightly more expensive and gives you a bit more bandwith with AC1750.
However for a small business consider a dedicated AP (access point) to handle all your wifi, the
Unifi UAP-AC-PRO should handle up to 127 client wifi connections max per-radio (127 on 2G and 127 on 5G, a theoretical max of 254 clients), and their single AP can be easily managed with their phone app. Personally I am using their UAP-AC-LR model on my Fios Quantum router (with the wifi on the router disabled of course), could not be happier with the performance and reliability, and no problems when we have family over to visit (where we can easily hit 15 devices in use at the same time).