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Jenelle Evans believes her kids are at great risk while under the care of her mother, Barbara, and it's all because of Evans' erratic brother, Colin, who has a lengthy history with the cops.

Police records -- obtained by TMZ -- show police have had at least 8 interactions with Colin since February. Colin has called to report stalkers at his home, possible break-ins, trespassers and made claims someone was putting chemicals in his water. He has even listed David as a possible suspect in the reports ... though no evidence seemed to support David's involvement.

Play video content 6/4/19 TMZ.com

There's also a report of a woman who claims Colin approached her and claimed she was taking photos of him and his house ... the woman was only taking photos in the woods. Police advised Colin to leave people alone.

Police have also responded to Barbara's home several times over the last few months ... including a disturbance call where a family member had thrown items in the home and issued threats.

Our sources say David and Jenelle will stop at nothing to get their kids back, and believe the dangers of being with Barbara and possibly around Colin are much greater than anything they'd face at home.