Make sure you have a good reason for the check. It will only be accepted to counter vandalism or disruption to Wikimedia wikis. Valid reasons include needing a block of the underlying IP or IP range, disruptive sockpuppetry, vote-stacking, and similar disruption where the technical evidence from running a check would prevent or reduce further disruption.
Be specific in your reasons. Ambiguous or insufficient reasons will cause delays. Explain the disruption and why you believe the accounts are related, ideally using diff links or other evidence.
Make sure there are no local checkusers or policies.
@6AND5: that still doesn't indicate the purpose of knowing that they are related parties. An interest in a relationship alone is not a reason for checkuser. There would be need for a proof of wrongdoing, circumventing votes, circumventing blocks, etc. — billinghurstsDrewth 07:03, 24 January 2015 (UTC)
The question is that the participant (Lakiditto098 (same 1221nor, Lilit1345, Karenpetrosyan)The following accounts are Confirmed) is blocked (unlimited), and now his brother allegedly began to write articles. --6AND5 (talk) 14:11, 24 January 2015 (UTC)
If it is his brother that may or may not mean the same IP address. It may or may not mean the same user agents, etc. There is nothing that we can do that is going to differentiate that sort of relationship and you will need to work it out for yourself. — billinghurstsDrewth 11:24, 25 January 2015 (UTC)
Member admitted he and his brother one person.--6AND5 (talk) 14:04, 25 January 2015 (UTC)
Thanks for getting back to us. Closed Issue resolved by community. — billinghurstsDrewth 14:05, 25 January 2015 (UTC)
User:Ruslik0, а можно показывать все новые записи этого участника в армянской Википедии ?--6AND5 (talk) 14:16, 24 February 2015 (UTC)
Confirmed Dmitryne, KuznecovGrigory, Ruþín16, OstapBinder, MedvedevDmitriy. He did a pretty good attempt to cover tracks. Almost had me missing it. I don't speak Russian, though I do speak CU and IP. <g> — billinghurstsDrewth 14:46, 28 February 2015 (UTC)
Reason(s): Conflicts and edit warring in articles related to and including fa:ملایر. Continuous disruption, even after sysop warnings. The users have so far broken the three-revert rule by supporting each others reverts.
Note:مادستان is highly suspected to be suckpuppet based on WP:Duck test. -- Nojan (talk) 00:07, 5 March 2015 (UTC)