Beis Din can have Layman as a Judge?

 Shulchan Aruch (CM 3) A Court of Law must consist of not less than three [Judges]1 and every [group of] three [Judges] is called a Court of Law even if they be laymen.2 For it is impossible that there should not be among them [at least] one who has a knowledge of logical inferences in [civil] laws.3 However, if there is not among them [at least] one [who has such knowledge], they are disqualified to judge.4 Nevertheless, they may receive the pleas [of the contesting parties] and forward them to one who is qualified to render legal decisions.5 They may try the defendant6 against his will7 if the latter8 declines to come down before Court,9 or he is not willing to attend the Court with the plaintiff in his10 home town.11 But if he is willing to attend the Court with him12 in his10 home town, only that he is not pleased with the three [Judges] whom the plaintiff has chosen, — then [the law is that] each [litigant] chooses one [Judge and the two Judges together choose a third].13 Gloss: As stated infra § 13. It seems to me [that this applies] only to Judges who are not permanent, but if there are permanent Judges in town he cannot say, 'I will attend Court in their presence only on [the condition that] each [litigant] chooses [one Judge and the two Judges together choose a third]'.14 Thus is the accepted custom in our town. , infra § 22, par. 1 end.

Beit Din and Dayanim

A bet din can’t function with less than 3 judges. These 3 judges can be any 3 people even if they’re not knowledgeable as long as one of them is familiar with the laws of judging.[32]

If none of the judges are knowledgable, the bet din doesn’t function unless they are the communally accepted bet din.[33]

Even though theoretically one expert judge can judge cases without any other judges, nowadays we don’t have an expert judge of that caliber.[34] However, if the one expert judge was accepted by the disputants and the case is simple, he can judge the case, otherwise an individual judge should not judge alone.[35]

The more judges on a bet din the better, though, the judges need to be fit to be judges.[36]

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