There is a lot of evidence connecting all of the companies mentioned in your question. There may be more connected companies that we are not yet aware of. From Wikipedia:

The first Changelly prototype was created as a startup in 2013 by the enthusiastic team of MinerGate, a mining pool, that has one of the longest track record in the crypto industry.

More evidence for the Changelly/Minergate connection has been reported by Monero users on Reddit:

There is a reason why you are not listed on getmonero.org. You are never responsive to questions and getting support is almost impossible unless you are willing to beg mods in the Minergate troll box.

Bytecoin, publicly launched in 2014 contrary to false claims of a 2012 launch but significant effort was expended prior to that time to develop the CryptoNote protocol, which is not based on Bitcoin. Due to their proven high familiarity with the complex CryptoNote protocol (at the time) nobody aside from the Bytecoin creators could be behind Minergate.

MinerGate was founded on 24th of March, 2014. It was the first mining pool for CryptoNote based currencies

Readers of Cointelegraph were surprised to learn that according to a former writer, they were funded by Bytecoin:

While some have cast doubt on my assertion, I have no doubt that CoinTelegraph was funded by Bytecoin from at least when I started and continues to get funding from the stable of CryptoNote coins, among other clients. My suspicion is that someone close to the Bytecoin team, perhaps the Bytecoin team itself, owns CoinTelegraph. But it could be as CryptoCoinNews P. H. Madore proposed, that they are simply funded by MinerGate, which they certainly have connections to.

More details on the connections can be found in this interview with Ian DeMartino, the writer quoted above. CoinTelegraph has partnerships with a number of companies which you did not mention, which could help explain why HitBTC is still listed on CMC, and why BCN no longer has a premine flag.

According to this 2014 Bitcointalk advertising opportunity announcement Coinmarketcap is part of "The CoinTelegraph Media Group"

Freewallet uses the Changelly API to facilitate cryptocurrency exchanges. They also introduce serious security risks typical of other Bytecoin and closed source Minergate affiliated services:

Also, they implement XMR wallets with your own unique address but they are holding the private key (from you), under the incredible justification of doing it so for "security" of the user.

Chainradar was launched in 2014 by imready2rock and shares data with Minergate. On Chainradar you will find price quotes "powered by HitBTC" and on Minergate you will find many banner adds for HitBTC. Both focus on CryptoNote coins and sometimes offer gimmicks to encourage users to download closed source software.

Read this answer about the failed attempt to force XMR/BCN merge mining shortly after launch. Combine that with more recent plans to promote merge mining with XDN. Only one Monero mining pool supports XMR/XDN merge mining. By this point which one should be obvious. The Minergate mining pool is also the one one that adds strange things to tx extra:

01c4230d59c83b3042fd82999cfda5be6b77c1673d9442d1f21c7ab9215bdc6c18021198414900000000000000000000000000000321004bff195014248ae22838853bcf293b8945f9baaac693c2d05bafe2f0f3e6c69e

The above test means that by mining on minergate you are "spamming the blockchain with whatever that crap is".

In addition to popular coins, BTC, XMR and DOGE, Fairproof supports the scarcely used XDN and BCN, which coincidentally were discussed above in the context of merged mining proposals. Minergate denied an official connection to fairproof when asked about running fairproof banner ads. However there is a lot of circumstantial evidence to counter than claim including website design and FairProof advertising in both the BCN and XDN Bitcointalk threads. Supporting hardly used coins when trying to run a successful business makes little sense, unless you have ulterior motives such as using them to promote merge mining with Monero, which is only offered if users download and use closed source Minergate software.

Based on similar circumstantial evidence such as design and an "Exchange rate provided by HitBTC" BTCLevels could also possibly be connected.