Internet Slowing down sometimes when other devices connect

Sometimes when i'm playing a game like league of legends, other people visit and they automatically connect to the internet with their phones since they have been here before and I gave them the Wi-Fi password. When that happens, my connection to the game completely drops, unable to play since its a online multiplayer game and it just attempts to reconnect. I either turn off my Iphone 6s Wi-Fi off to have the internet working about but sometimes I have to turn multiple devices Wi-Fi off. All the phones are being unused and it still affects the Wi-Fi. My internet specs are 25Mbps down and 2Mbps. Is there anyways to fix this?

Cabled ethernet is faster than Wi-Fi, and the data rate you show is based on ethernet.
When other devices are connected to the internet, the router switches from line to line for a shared bandwidth.
Online gaming requires a high bandwidth, and multiplayer even more so.
Even unused, the system is checking each. They can turn off their phones or Wi-Fi connection when you are gaming.

Easy fix, change your Wi-Fi password and don't give it to anyone. TONS of cell phone apps/services rely on a Wi-Fi connection and if someone comes over who doesn't typically have a Wi-Fi connection, will start to update all those services now that they have Wi-Fi.

Clean up your network, change the password and don't hand it out.

I would guess at two things.
1. Your Wi-Fi is not Password protected, so as you say anyone can log on.
2. You have a CABLE internet connection. Cable internet is a "Party" line of sorts. Unlike DSL which is a Dedicated Subscriber (Phone) Line. You share the Internet Provider with EVERY home and business between you and the Cable Providers office. That is why Cable advertising fantastic speeds, which you will never attain because of all the other traffic. When you see those ads on TV, that is a single "user" directly connected, with no other parasites (users) on the line.

Get rid of the Wi-Fi, get a hard wire (LAN) cable if your going to play MMO games on-line.

Then there's also the possibility you have a Virus/Malware too.
And, does your machine really have the "Recommended" specs for the game(s) you are playing…

You should also check when playing, that all background operations are stopped. Your email, and programs are most likely each checking for updates and maybe even defragging while you play unnoticed.

As Dave says, change the Wi-Fi pass phrase and don't give it out.

There are three reasons why gaming can be affected:

1) When your friends' phones connect, they may automatically start downloading updates, email or social media notifications. This is using up some of your ISP or Wi-Fi bandwidth. The ISP connection and the Wi-Fi connections are both shared interfaces so the more people using them the less your share will be.

2) If one device that is connecting to your Wi-Fi is supporting the older slower Wi-Fi standards, particularly 802.11b, and not supporting the faster ones, then this will slow the whole Wi-Fi network to their slow speed. 802.11b will have trouble getting above about 6 Mbps.

3) Many online games require short ping times (small lag). If your packets are having to queue to use one of the shared interfaces (ISP or Wi-Fi), then your lag figure will increase and upset the game.

If you want to give friends access on a conditional basis, after you have changed your Wi-Fi pass phrase (assuming it is WPA or WPA2), get a TP-Link TL-WA850RE Wi-Fi range extender. Set it to connect to your network and set its extension network name to be different from that from your router. Next go to:

https://www.wireshark.org/tools/wpa-psk.html

and enter your router's pass phrase but the SSID of the extended Wi-Fi network (not the SSID that the router is using). This will give you the 64 character encryption key for the extension network, which will be different from the one for the router's network. Give this key to your visitors and they will be able to connect only to the extension network.

You can use the router's pass phrase on both the router's and the extension networks as the pass phrase, unlike the encryption key this will be the same for both networks.

When your friends call, if you want to give them access, plug the extender in to a power outlet. Unplug the extender to lock them out again.

The other advantage of using such an extender is that the bandwidth available on the extended network is typically around 50% of the bandwidth on the router's network.

You shouldnt play games over Wi-Fi.Wi-Fi has got complicated.Old devices do it one way, new ones do it another and superfast ones do it completely differently. Your one router can't cope with all the mess of signals. Your router may be DUAL Wi-Fi signal capable, turn on the old slow one, and let them have that instead. Get yourself a LAN cable.