Is a man subject to mobilization who is the father of 3 children, of which only 1..

According to Article 23 of the Law on Mobilization Training and Mobilization, conscripted women and men who have three or more children under the age of 18 are not subject to military service during mobilization.

If you meet the above criteria, you are not eligible for military service. Even if the children do not live with you. The main thing is that you support them (for example, you pay alimony).

As for a disabled mother, according to the same Law, conscripts who have a wife (husband) from among persons with disabilities and/or one of their parents or parents of a wife (husband) from among persons * are not subject to conscription for military service during mobilization with disabilities of group I or II*, provided that such persons with disabilities do not have other able-bodied persons obliged by law to support them.

That is, the mother's disability will not be a reason for exemption from military service.